 When they get a new supervisor, the new person might not get along with the person who's fired or feels threatened by them. The second reason falls along the same lines. Perhaps there's a change of ownership or management. This can lead to shuffling around and anybody is on the chopping block. The third reason is you are becoming a burden on the company, even if it's for something legal like taking a leave of absence. But at least then you have the law on your side. Brian VanMiller, CBS News.