Lots of aspects make coaching/running youth teams so difficult, players not being consistently available is my biggest gripe but anyone who puts so much of their time into doing something for no money and much more importantly no appreciation they deserve respect and support not crtiscism.

When you stop enjoying it. When the passion wanes that is the time to pack in.

In my opinion and experience it is the opportunity to work with knowledgeable trainers to further my own education and more importantly to watch the players develop, as players and as people.  It is also the feeling of contributing to the success of the local high school teams by keeping the majority of my players from the local community.  Having done this for a while now, seeing some of the players from my first team that now have families of their own, becoming volunteer coaches is very gratifying.  Others have become teachers and successful high school coaches.  When you run into them and they give you a big hello and ask how you're doing it makes your day.  Basically it's the people and a passion for the game.

When you're doing it for free, your rewards are often not immediate. As someone else pointed out, seeing your former players doing well in high school or on older club teams really makes you feel good. For me, as long as they want to come back and play again in the fall, I've probably done more good than harm and some days, that just has to be enough!