Perfection

Nobody can be perfect - but trying to be so is  the only way to keep getting better

A perfectionist is the one who keeps getting better but is always sad about not being perfect
A negative person is the one who does not start off to get better offering the excuse that nobody is perfect anyway
A positive person is the one who understands he cannot be perfect but uses it as a means to keep getting better

As time progresses:
The perfectionist will be much better but will never be happy about it as he can be still better - He is trapped in the future
The negative person will remain stagnant always and will become even more negative when he realizes how much he has already lost - He is stuck in the past
The positive person is always happy with what is, and keeps making better choices to determine what will be - He is rooted in the present