i'm very naturally competitive. i think that's my main motivator. coupled with that, i try to keep company with golfers who are better than i am. two of my favorite people to play with are both scratch players, and i very, very rarely beat them, but it keeps my competitive drive sharp and keeps me trying because i see it as a goal, being able to beat them. it also really helps to highlight where i went wrong during the round. i can hit the ball every bit as far as they can, i can (usually) make contact that is just as clean as crisp as anything they hit, but the big difference is when they miss, they only miss by a few yards, ie, the flag is on the left side of the green and they landed on the right side. my misses aren't quite so acceptable. as far as breakthroughs, i honestly can't recall any one thing that suddenly turned it around for me. it was just practice, practice, practice and my body gradually learning the motions that it needs to make in order to deliver the club back to the ball squarely, although i will say this: confidence is EVERYTHING. if you find yourself standing over the ball and having thoughts like "am i aiming left? i feel like i'm aiming left..." or "gosh, i hope i don't shank this one" or "i hope i have enough club," then the odds are very heavily stacked against you making the swing you need to make. my best shots come when i step up to the ball and, if i think anything at all, it's just simply a "yup. i feel a good swing coming up."
and mind you, i'm not talking about giving yourself a pep talk before each shot and trying to induce confidence. it's pure confidence that you get from practicing and playing enough that when you walk up to your ball, you look at your target and you think "psh. i've hit this shot a thousand times already. i know this shot. i've got it in my bag."