Joining a new company is an interesting event: you're basically an outsider, trying to see if you fit in or not. And sometimes, this period makes or breaks the overall situation. After all, humans have a sense of belonging. And if you fail to integrate and continue to feel that you're an outsider, then this isn't a situation you want to be in.
See, when one joins a new company, there are plenty of questions. There are things you just have to learn. How things work differ from one organisation to the other. And knowing these things just take time. There's also the people. Sometimes it is hard to integrate because the people who are already there are territorial and they don't want to open up. And sometimes the environment is just very different that the new person is suddenly immersed into a sink-or-swim environment.
I know two people who started a new job at the same time, yet at two different companies. One of them started getting bored after two weeks, because things were rather slow to pick up. The other was already panicking, because there's just so many things to do right from the get go, and of course, this person made a few mistakes along the way, mostly because this person was new and didn't know how things typically run.
This just emphasises the importance of good onboarding. Alas, sometimes, managers fail to see this, and the new colleague is left in the lurch. The funny thing is that none of these points are specific to the corporate environment. People act the same way in other social circles. If you move to a new country, as an expat, typically what makes or breaks the expat experience is whether you feel at home or not in your new adoptive country. If you always feel like you don't belong, then sooner or later you'll just leave and go somewhere else.