...To dwell on the past, look to the future and let go of what you can't change.
...Spend time thinking about the what if's, bad or good, don't think on the what if's, just live for the moment and enjoy life.
...Have regrets, if you are thinking about doing something, look at this way. If, in 60 years time you will look back and regret something, do it now, while you can.
...Hold grudges, if somebody doesn't treat you right, rise above their pettiness. Forget about the ones who want to cause misery and find what makes you happy.
...To spend time trying to please others, surround yourself with happiness and if people don't like you, rise above it, you can't please all.
...Worry about things that are out of your control, if you can't control it, why worry? Obviously there are some certain matters that you will naturally worry over such as exams and such, but even your attitude to that sort of thing can be changed with good preparation.
Do you agree that life is too short for these things?