Donald Knuth wrote “premature optimization is the root of all evil” in 1974, in a paper called “Structured Programming with go to Statements”. It’s high on the leaderboard of the most quoted sentences in our field, and I would wager that only a fraction of the people quoting it have read the paragraph it comes from.
Here it is, with the part I think is important but quite often missed:
We should forget about small efficiencies, say about 97% of the time:
premature optimization is the root of all evil.
Yet we should not pass up our opportunities in that critical 3%. A good
programmer will not be lulled into complacency by such reasoning, he will be
wise to look carefully at the critical code; but only after that code has been
identified.The argument is about where to spend your effort. Don’t waste your time on code that doesn’t matter, find the code that does, and then optimize the hell out of it. In the very next sentence he explains how you find it. Of course you measure, because “the universal experience of programmers who have been using measurement tools has been that their intuitive guesses fail”1.
That’s not what the sentence turned into, of course. Culturally, “premature optimization” became shorthand for “don’t optimize”, and the word premature becomes irrelevant. Someone suggests making a thing faster, someone else recites the sentence, and the conversation is over. This happens without anyone having established that the optimization was premature, or what premature means (presumably we’ll get to it when the first requests start timing out).
This post is not about that, though. Instead, look at it as a historical precedent, because I think the Bitter Lesson is going through the same thing right now.
What Sutton said
In 2019, Rich Sutton published a short essay called “The Bitter Lesson”. It opens like this:
The biggest lesson that can be read from 70 years of AI research is that
general methods that leverage computation are ultimately the most effective,
and by a large margin.He walks through chess, Go, speech recognition, and computer vision. Each time, researchers built what they knew about the domain into their systems. It helped in the short term, then it plateaued, and eventually it lost to methods that leaned on ever-cheaper computation. His verdict: “The two methods that seem to scale arbitrarily in this way are search and learning.”
It’s a good essay, and I agree with most of it, begrudgingly. But a few things are worth pointing out, because, again, the nuance tends to get lost.
Sutton isn’t saying that algorithms don’t matter. Finding methods that make good use of computation matters a great deal! He also isn’t only talking about training, since search at play time is one of his main examples. And the claim is about how to build methods that keep improving as computation scales, not about every system those methods end up in.
But it’s also a pretty constrained essay that leaves many things unsaid, and people are starting to put words in its mouth already.
Unsaid things
The thing I see most often is a slide from general methods to general models to general systems, as if they were the same thing. A general learning method can produce a very narrow model. A general model can be used to train a specialist, for instance by fine-tuning it on a single task, or by using it as a teacher for a model that only ever sees that task. And none of this says anything about whether the hardware it runs on should be general. That would required quite a different argument.
The essay also isn’t a theory of cost. It doesn’t tell you to run a large generative model when a small classifier does the job. It doesn’t tell you how to weigh one training run against the billions of inferences that come after it, or when the cost of keeping a system general starts to exceed what you get out of it, or when engineering effort pays for itself in operating cost. This is hard, bespoke work, and only tangentially related to engineering (though it can be influenced by it).
A method that scales better is not necessarily a system that’s cheaper to run. A general method might be the right way to find a solution, and a specialized system might be the right way to deploy and run it!
I’d argue that the choice between the two is mostly economic. Generality saves you from engineering each solution separately. Specialization can save you recurring cost. That matters more as a workload becomes predictable and its volume grows, because the engineering cost gets amortized. This is true for software, for models, and for physical machines, with very different numbers attached to each, many of which I don’t know, because my expertise is pretty narrow in this domain.
Specialization doesn’t always win, of course. But we should do the calculation and apply diligence instead of just assuming the answer. If anything, general learning methods might make specialization cheaper, because they let us derive the specialist from the generalist instead of building it by hand.
Folding napkins
I got here for a reason.
A few days ago I listened to the Latent Space interview with Jason Ma of Dyna Robotics. Dyna adapts one large generalist model to new tasks, and their biggest deployment folds thousands of napkins a day at the restaurant chain Din Tai Fung. When co-host Vibhu asks whether a specialized machine couldn’t do that, Ma answers that napkins are deformable, and that adapting a general model gets them to production quality faster. A few minutes later, swyx sums it up:
The term that comes to mind is kind of like bitter lesson for robotics,
right? You, instead of the specialized robots, which is a lot of industrial
engineering, you build a generalized platform that can- Do a last-mile
fine-tuning [...]Nobody reacts, but Ma’s reasons are about developing the capability, and swyx’s summary is about the machine. And the important part, I think, gets dropped, namely what it costs to operate a general-purpose robot at a napkin station, day after day, for years, with many of its actuators and sensors disused2.
And deformable objects are hard, sure. But the robot isn’t folding napkins on the back of a moving truck. It’s standing in the back of a restaurant, in an environment someone controls.
As I understand it, specialized machinery usually works by changing the environment until the task is simple enough for a simple machine. If we skip that step, I think we’re arguing that an early Ford-style assembly line staffed with humanoids beats a dark factory full of stationary robots, each built for one job.
For what it’s worth Boston Dynamics went the other way with Stretch, their warehouse robot. They built “a simpler robot” for the job, “with pieces from Spot and Atlas”, while Atlas continues as a separate humanoid project. As far as I can tell, the generality there lives in the process that produces the machine rather than in the machine itself.
Just scale it
This is, then, what actually bothers me. Someone points out an inefficiency or a limitation of an architecture, and proposes looking into a different approach. Someone else says “just scale it”, or “hand-engineering doesn’t work”, or simply “we’re Bitter-Lesson-pilled” (I’m way too old for this, by the way). From there, the conversation is dead in the water. Throw in some Knuth if you want to, we’re arguing from authority from here on out.
These statements borrow authority from a historical observation without showing why it applies to the problem at hand. And they invert the burden of proof. The person proposing an optimization now has to argue against the presumed inevitability of scale, while the person advocating scale doesn’t have to show why it’s the better answer right here, right now.
It’s become a bit: instead of using Sutton to question our architectural intuitions, we’re already using him to defend the status quo.
The irony
Sutton’s essay is, at its core, a criticism of researchers getting attached to their own ideas about how intelligence works. He even names the mechanism: “There are psychological commitments to investment in one approach or the other.” And then:
We have to learn the bitter lesson that building in how we think we think does
not work in the long run.I think the meme risks encouraging attachment to a different set of ideas: that generality is always desirable, that scale will fix present architectural problems, that specializing is a lack of ambition, and that engineering effort is wasted if computation could theoretically learn the solution.
That’s basically the failure Sutton described. And because the original essay is genuinely insightful, its authority makes the new dogma harder to question, even if they just absorbed the headline.
Fin
Of course I don’t think the Bitter Lesson is wrong, and I also don’t think everyone invoking it misunderstands it. My problem is that its authority increasingly lets people skip thought, the same way Knuth’s sentence did. Both essays ask for more work, not less! Knuth argues for measuring before optimizing, Sutton for checking our intuitions against what actually holds up as computation grows.
So, instead of arguing about it, let’s do the work.
Footnotes
1. A paragraph earlier he goes even further: “In established engineering disciplines a 12% improvement, easily obtained, is never considered marginal; and I believe the same viewpoint should prevail in software engineering.” I aim to be as unapologetically pointed in my arguments as he is one day.
2. I’m not a roboticist. I’ve never built a robot that does anything useful, and I’m sure people at Dyna have thought about unit economics a lot more than I have. My complaint is about the shape of the argument, not about their business.