but if you just sit down and play them over and over, you learn the sticking points and eventually you pull out a clean run. There's usually a tricky spot or two where in order to get through one section, you have to set it up in a section prior, like making sure you land on a certain down slope in order to have the speed to make a big jump after, or hitting a rhythm section just right so that you have the speed to clear all gaps. Occasionally it pays to come to a complete stop, totally reset your momentum, before clearing a gap or hurdle (on Extreme this is a much more useful skill). Eventually you just learn the rhythm -- gas here, lean here, sometimes a brake, make sure rear tire makes contact with this surface here, etc.

And yeah, once you're on Hard everything except for the Advanced bike is generally not good enough to clear the course.

And sometimes the Skill Challenges can be a great way to learn when you're new, in particular the hill climb ones, because those really force you to learn how to lean and gas in order to get past sticky parts, and as you do it over and over you can start to recognize the patterns.