I was trained as a pianist throughout my school days, and did not accept a piano scholarship, I'd had enough by then. I read both clefs like the newspaper, was thoroughly grounded in it all, and strangely deaf as a post in terms of matching pitch vocally early on, the ear training was quite a leap.
I always wanted to rock. I'm wired by DNA to hear bass, it's innate. So I decided I'd learn, innocently telling myself it would be like learning to type: I knew spelling, punctuation, etc., I just needed to learn the typewriter, so, I'd transfer my musical knowledge to the bass, 'what the hell, it's only one note and one hand at a time. Easy !' Well, it didn't quite work out that way, but then it did.
Of course, all the theory transfers, but like anything in life, to get really good you spend the time and dig deeply into the minutia and the tiny details, and that takes a while ( . . . .still to this day . . . .), and unlike classical music, so little of it is properly written out or transcribed in a really half-ass way, so that's rarely much help.
Then it really took me a while to wrap myself as to the scales or finger positions 'overlapping': Do I play this E on the A-string, the D-string, up HERE, down THERE, etc., I was welded to seeing the scales in the linear fashion we see on a keyboard. It's actually an advantage ultimately, as you have more ways to play a given figure, but it took me a long time to 'get it', and ultimately the biggest reason I went to five-string was I could play a two-octave scale across the fingerboard in one position without shifting up or down the neck, it seemed more keyboard like to me.
To me it's far more creative and far more intellectually challenging to sit in that spot between the drums and everybody else and make it all work, one note at a time.