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Published · transcript-backed

Lenny Rachitsky: uncertainty

23 Oct 2025 Lenny's Podcast Al Engineering 101 with Chip Huyen (Nvidia, Stanford, Netflix)

“Something that Hamel and Shreya shared is that people need just, I don't know, five or seven evals for the most important elements of their product.”

— Lenny Rachitsky

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Speaker
Lenny Rachitsky
Attribution
Verified speaker
Claim type
uncertainty
Recorded
23 Oct 2025
Publisher
Lenny's Podcast

Transcript context

…You don't have to be absolutely perfect, I think, to win. You just need to be good enough and being consistent about it. Okay, this is not a philosophy I follow, but I have worked with enough companies to see that play out. So when I say, why a company don't eval? Let's say you are an executive and you want to have a new use case. So here's a use case you started out, built and it's like it works well. The customers are somewhat happy. You don't have the exact metric for it. So the traffic keeps increasing, people seem happy, people keep buying stuff and now here's our engineer coming like, "Okay, we need eval for it." And it was like, "Okay, how much effort do we need to go into eval?" And they were like, "Okay, maybe two engineers, this much, this much." And it could maybe would improve that and it was like, "Okay, so how much expected gain can I get from it?" And the engineer would be like, "Oh, maybe you can improve it from 80% to 82%, 85%." And it was like, "Okay, but [inaudible 00:25:35] that two engineers and we going to launch a new feature, then it could give me so much more improvement." So I think it's one of them is eval. Sometimes people think of eval as like okay, this is good enough, just don't touch it. If you do spend a lot of energy on eval, it would only incremental improvement where it spends the energy on another use case and maybe [inaudible 00:25:55] good enough that you can vibe check it. So I do think maybe that's a debate is about. I do think that a lot of time people just get things to the place where it's like, okay, good enough, people run. But in the end, but of course there's a lot of risk associated with it because if you don't have a clear metric, you have a good visibility to [inaudible 00:26:17] applications or models performing it might do something very dumb or it can cause you, I know something crazy can happen. So yeah, so I do think eval is very, very important if you have, if you operate a scale and where failures can have catastrophic consequences. Then you do need to be very tyrannical about what you put in front of the users, understand different failure modes, what could go wrong and also maybe in a space when that it's a feature, the product is a competitive advantage. You want to be the best at it. So you want to have a very strong understanding of where you are and where you are with the competitors. But it's just something that's more a low-key, okay, this is like something is like, okay, that's not the core but it helps with our users. Then maybe you don't need to be so obsessed or theoretical about it. It's like, okay, that's good enough for now and if it fails, then it fails. Okay, I know it's so terrifying. But yeah, I think it's all about the question of return investment. I'm a big fan of eval, I love reading eval. And I says, I understand why some people would choose to not focus on eval right away and choose bringing on new functionalities instead. Awesome. That is a really pragmatic answer. What I'm hearing is evals are great, very important, especially if you're operating at scale, but pick your battles. You don't need to write evals for every little feature. Something that Hamel and Shreya shared is that people need just, I don't know, five or seven evals for the most important elements of their product. Is that what you see or do you see a lot more in production that people build and need? I don't think of just a fixed number on the evals. What was the goal of eval? The goal of eval is to guide the product development. So you see eval, because I think I'm a big fan of eval, is that it helps you uncover opportunities where the progress are doing well. So sometimes, we've seen a very obvious [inaudible 00:28:15] where you look at the eval and we realize it's like, okay, it performed really poorly on this specific segment of users and then we look into it's like, okay, what's wrong with it? And it turns out, it's like we just don't have a good messaging to it. So people should just focus on the things that we're doing poorly, can improve significantly. Yeah, so I kind of like the number of eval is really depends. We have seen product with hundreds of different metrics.…

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