I learned a lot in 2 years working at a startup. I really cut my teeth there, learning lots about engineering, design, business, and people.

The most valuable thing I learned though, was how to know when it’s time to leave.

The thing is, startups ask a lot of you. You sacrifice enormous amounts of time and energy — two things in limited supply that must be siphoned from somewhere. More often than not those places include your social life, time with friends and loved ones, sleeping, and recreation. Depending on your level of commitment and their level of demand, anything can be up for grabs.

That’s the nature of the beast, but there’s a reason people do it. It’s exhilarating, and, if you’re in the right place and have the stomach for it, so worth it.

The catch is, you have to care. It can’t just be a place you punch in and punch out of. You have to be burned up by the problem you’re aiming to solve, because in the end, that’s the only thing that will keep you moving.

The money, the often-crazy promise of fame and fortune, and the cozy office with the yuppie juices won’t be enough to justify the amount of your life poured into your work. Only being so frustrated by a problem that you have to solve it will see you through the hard times — the troughs in the emotional roller coaster where it seems certain your company/product is doomed to failure and obscurity.

If you care enough to get through the rough times, that sort of life can become addicting (if you are so inclined). That addiction can obscure your original motivations and make it hard to remember why you were working so hard in the first place.

But, eventually, when you get a quiet moment to breathe and realize that the problem you and your colleagues are trying to solve is no longer one that you can’t help but try to solve, that’s when it’s time to go.

Leave for yourself, certainly, but, if you ask me, you owe it to your colleagues who depend on you to kick ass everyday to leave when you can’t bring yourself to care as much as they do.

To linger, gradually becoming complacent and comfortable, will only lead to harsh feelings, burned bridges, and wasted time.

It can be bittersweet, especially if you love the place, but it’s a fact of life that people change and start to want different things and acquire different motivations. Don’t fight it, enjoy the time you spent for what it was, the lessons you learned, the things you managed to build, and move on taking it all with you.