Not original to me, this graph of ability versus knowledge (which has to be felt, rather than passively acquired), but unfortunately I don't have good internet access presently and cannot find where I saw the idea a couple of years ago.
Basically, it illustrates the big long periods where there is no progress, then suddenly there is a big leap forward.
Of course, almost immediately you are unhappy again as your knowledge and taste outstrips your ability quite quickly - again and again and again . . .
Sadly, everyone seems to have to go several of these episodes before producing anything vaguely respectable and the whole process is so disheartening many give up.
But every book that I read and really try and understand, every time I go to a gallery and critically appraise the paintings something changes. It just may not be clear what or how for ages and ages. Trying new stuff has the same effect (but possibly even more so) - the gap between drawing the view from the library and painting it was rather a long one, for example.
So really, just have faith and keep going . . .