Some things may take years to have them figured out. It is when someone shows you a definition of some "basic" mathematical object, but does not say why is this defined this way and how should it be interpreted. Moreover, you won't find the answer to your "why" and "how" questions so easily either because they are "so simple" that noone cares to tell, or simply because noone cares. Some time passes and you forget your desire to find out the meaning and just get used to the definition.
For example, it took me some months after I first heard the definition of matrix multiplication to understand why was it defined precisely like that. Same with the notion of a "determinant". Same with pretty much any other university's first-year mathematical object. The problem is probably in the fact that many of our math courses are "definition-based", not "intuition-based", but anyway, that's not the subject of this post.