what are the reasons for adsense suspending an account

I have not got a clue as to why many accounts are being suspended. I am disgusted that after work i have done now seems to be a waste of my time as the accounts are getting suspended. There has not been a reason as to why this is happening, well not one that i have seen anyway. I wish that they would put information out there to say what the problem is and if this account will come back or not. Surely we have a right to know what is going on.