I was thinking the same but B-Gas said it so much better. Don't be afraid to lose reader sympathy, as long as your character has just one redeeming feature, you probably won't -- he might just intend to do something good, and that's enough.
Seije - I think you're selfless character could easily be flawed. Rather then getting himself into trouble because he waits too long to defend himself as a result of low self-esteem; why not have him hesitant, fearful of taking action and prone to procrastinating? Thus action is pushed upon him rather then chosen by him, that's more befitting of a low self-esteem character - sticky situations here we come! And low self esteem doesn't lend itself to helping people because the character's mindset will be "I'm useless, therefore I can't help". A low self esteem character is more often then not a 'wet blanket' and an annoyance to other characters - not the self-sacrificing type you describe. You want to steer away from superficial low selfesteem 'What if I can't? Oh look I can' and really think about the way that feeling of worthlessness might affect a character's decision and actions. Obviously all this is just my humble opinion.
