My answer to that would be there is so much pressure around us. Perceived? Real? Maybe. Whichever. It is there. It dictates upon us how we act, how we react, how we deal with things, how we accept or reject things.
Often times, deep inside we are screaming for help. Without wanting to say anything - for whatever reason be it pride or fear, whatever - we decide to silently scream hoping that somebody would hear us. Ironic. We want to be heard but we refuse to be heard.
And we want to give our all, still. Maybe because we need to please. Or want.
Bottom line is we must realize when enough is enough for us. When should we say no more. After all, whose life is it to be lived anyway? Assess our reasons and motives. Do not be selfish but do not be selfless. Live enough. Do enough. Too much of anything can never be good, after all. Moderation may be an appropriate word. Do because you want to but do the right thing. Bad will never be replaced with anything good.
In the end, it's a matter of finding oneself. Of realizing when you've done what you had to do and you should not do any more than what you cannot do.