If you are a sweet person who cannot say NO, people take advantage of you.
If you are not in good books of the manager, you shall suffer your life in getting leaves and permissions.
At times your career growth completely depends on how friendly you are with your manager (Only some times).
No job security, one mistake and the company can terminate you without considering your experience or knowledge (happened with few of my ex-colleagues)
If you are a more friendly person, you become a hot topic to gossip, we need to know our limits and play smart.
We can never trust anyone.