You're way off. There's a huge diminishing return on how much you can learn at a single job. From my own experience, I'd say it peaks around 6-12 months. There

You're way off. There's a huge diminishing return on how much you can learn at a single job. From my own experience, I'd say it peaks around 6-12 months. There's some longer-term things you can only learn by being at the same company for a long time (such as "how to grow a startup from 1 to 100 employees" and what comes with that), but those things are usually outside the realm of what software engineers interest themselves with. If you're spending more than 2 years at the same company, the only domain knowledge you're growing is that of how to be an employee at that particular company, and very little of it is very useful outside of it. Things like "I know how all these Facebook internal tools work inside-and-out". Cool, we don't have or need them cause we're a totally different company, now what? Whereas a lot of even surface-level knowledge can bring a huge amount of unique perspectives and solutions. And my own most successful projects have been the results of combinations of experience in multiple domains at once. And none of this prevents you from actually developing deep domain knowledge. For example, I have NOT held the same job for a decade and a half, but I HAVE been using Python (and other various software) for all that time, in a large amount of very varied situations, and I absolutely have "deep domain knowledge" there.