For me as early as high school it was easy to understand the concept of molecules having 3D structure (the standard textbook explanation of left glove versus right glove is easy), but it was really difficult for me to visualize it. I was not and am still not a visual thinker. This caused me a lot of problems when I needed to distinguish between enantiomers. For example I had a great deal of trouble when given two molecules that only differ in chirality, which one is levo and which is dextro, despite studying very hard.