Trials 2: Second Edition. It's a combination of muscle memory and sheer determination. It took me hours of practice (i.e. failing over and over again) to become good enough to start not falling on only the medium difficulty tracks. Next, I fell over and over to become good enough to complete ANY of the hard tracks.
70+ hours of playtime in, and I'm certain I will never beat the last few hard levels. I've seen videos of people doing them... they're long and incredibly difficult-- and I can only get past the beginning parts once in every 100 attempts or I can't at all.
Trials 2: Second Edition, I will never beat this game; it's very near impossible for me. I swear those that have beaten it (without falling, no less!) either cheat, mod the physics of the game, are epic naturals at the game or have played the game for over 500 hours. At least, that's what it seems like while watching them own the hard levels' faces.
On the other hand, I haven't reached the later Dark Worlds in Super Meat Boy yet... I'm a bit afraid.