1. Not everyone wants to be saved.
You can't help someone who's unwilling to receive your help. If someone isn't able to make a choice to self-help, chances are that they don't want you to aid them either. While your heart may be in the best of places, you can't leave the floaties on forever. Eventually, we all hit our sink or swim moment, whether it must be forced or voluntary.
2. Sometimes your resources aren't extensive enough.
People occasionally need things that you may not reasonably be able to provide. Not every problem can be solved with a little cash or a few favors. Some people have to commit themselves to their own ritual to overcome what they're going through. That requires self-control and commitment: things you can't simply provide for them.
3. You can't play God.
You're not in control of the outcomes that occur in everyone's life. You may care deeply for them, but you can't be the deciding factor in how their life goes. You don't make their choices or choose their consequences. Everyone has a purpose in their life, and that purpose is to be lived through their free will. We only have to be responsible for our own lives in the end.
4. You have to care for yourself first.
As selfish as it may seem to someone always wanting to help others, you have to allot yourself some self-love. You don't have to put all your time into everyone else's problems. Think about what makes you happy rather than everyone else. If everyone else deserves it, why don't you?
5. Their choices were their own to make.
You simply have no control over where someone takes their life. Each person makes choices everyday, knowing that the consequences are theirs to accept. When you make decisions, you can't expect everyone else to pull you out of whatever mess you stumble upon. Why teach them to lean on you as a crutch?
In this life, you're responsible for you. If you help some people along the way, good for you; however, don't try to be a saint. You end up being dragged down along with those you support through their toxic decisions. You don't always have to be cheering someone else on. You deserve happiness just as much as everyone you try to provide it for.