It is an extremely difficult thing to accept that one should not think of one's identity and aim in life by their employment, isn't it?
It really isn't. Why would you even begin to think in that in the first place?
Then there's the vicious reward cycle. Do something right with work and you're rewarded with praise, with positive feedback, with kudos. Do something wrong and... well you see where it's going. It's more subtle than how I train my dog, but not much.
And then the tech world is in awe to entrepreneurs and startups, where long hours and being defined by passion for what you do and it being the sole calling in life are the norm. You or I, older now I suspect (I certainly am) may look at it and shake our heads and think of the failed relationships we've seen (the same in any high-powered area of work), but for people without that view it's not easy. I had the same way of thinking as the OP, and even now I still get jealous of those who achieve much by having their work as their identity and aim in life.
And finally society again. There seems to be a growing expectation this is the norm and the right way, like the acceptance that single parent families are normal and a good way for children to be brought up (don't argue with the subject, think about how long that's been an accepted view). For ambitious, maybe insecure graduates starting out in work, that's a huge sense of competing to 'get to the top'. Why they're not sure, but it sure gives one an identity... or does it?
My only real life regret is that I didn't realize it a bit sooner.