If you went back in time to stop yourself doing something, then would that change the future? If so you would create a completely different future, one where you may not have the opportunity to go back and create it again by stopping yourself doing something. Of course you also wouldn't know why you ought to stop it because you would never experience the bad consequences of it because the you from the future who did experience them stopped your past self and thus created a new future and a new you.

If, however, you cannot alter the stream of time, and the future is the past to the future's future, then you going back to stop yourself doing something will always have happened and when you go back to do it you will remember being young and seeing your future self warning you, thus nothing will change; either your past self will do it regardless of your efforts or something else entirely will create the bad situation you wished to avoid in the first place.

Of course there is always the possibility that time travel is not possible, but that is no fun at all is it?