What do you consider a "reasonable" amount of time? (I probably come from the opposite viewpoint: I consider the few axes along which I've devoted over a decad

What do you consider a "reasonable" amount of time? (I probably come from the opposite viewpoint: I consider the few axes along which I've devoted over a decade to learning as being the particular high-dimensional corners making me me, rather than any of my 8 billion other conspecifics)