I am a perfect example of one of those people that knows the game of football well, but has a consistently terrible record in FPL.
Whilst luck plays a small part mainly with captain choices, the best players can do the simple things consistently that most of us can't. They are; not drinking and tinkering, being patient, keeping transfers to a minimum, not taking pt hits, setting and following a plan for future transfers, and not panicking due to stats and information found on sites like this one.
I know I for one can't do any of those things, but then I don't claim to be a great FPL player, and have only ever played to compete in my cash league, and disregard overall rankings.
This game is about discipline as much as anything, as if you can be disciplined enough to do all the things I listed, I think anyone with even a general idea of the game and players, coupled with the net as a research tool, can compete quite well in the overall rankings.
One season I may just challenge myself to make a serious effort overall, and try implementing the discipline side of things.
EDIT: Oops, sorry mod, I must have submitted the post at the same time you did yours. Feel free to move it with the rest.