Honestly, there are two main things I've seen junior devs get shocked by and I've written about both of them before. I'll give a quick summary here and link to the previous posts.

The first big issue to watch out for is [self-crunching when you start]. I know how much a new hire will want to prove herself, especially when it's your first job and you're a super passionate, driven youth without a lot of other responsibilities and something to prove. However, self-crunching ends up setting unrealistic productivity expectations in the eyes of your boss. If you ever ease off the self-crunch, it will look like your productivity is falling for no reason. If you ever need to crunch with the team later (and you probably will), it's an express ticket to burnout city.

The second thing to watch out for is the realization that [you won't get to work on your own ideas] for a long, long time. Your job is to make other peoples' ideas real - the director, the lead, the senior dev are the ones coming up with the ideas. You won't be creating the new systems, you'll be the one to make them work. You'll spend a lot of time learning. A lot of the things you thought you knew as a gamer will be proven wrong by the realities of the industry because it is a business.

The game industry really isn't for everyone, but it can be really fulfilling if you enjoy solving interesting problems and seeing other people enjoy your work. It really isn't a place that gravitate around a handful of stars, but a collaborative team environment where everybody works together to build something really cool.
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