There's the magic...some few of us need no time, care, nor constancy to find level. And unlike Stephen, I cannot place any ability to "see" level on work experience.
I was born with it, and it has been both a gift and bane from my first awareness.
Some years back, Stig in a pm to me posited that, given the relatively (to him, and agreed by me completely) low number of fells that my work has set before me, that I must have an unusual level of native talent...seeing as I seem to be able to accomplish advanced cuts without thousands of fells to earn the skills.
Stig, if my memory differs from yours, please say so.
In any event, I think being able to perceive level (simple), and to be able to visualize where the tip of 36, 42, or 60 inches of bar is and what it is doing deep inside a tree that well exceeds those dimensions (much harder), is a talent that cannot be easily learned. I'm sure it can be, but how??...Not so sure. It's a three dimensional puzzle at it's most simplistic description.
It is, as I said before, a gift. I cannot say I am better at it than most because I worked for it...just supremely lucky to have been born with the magic insight.