From personal experience I would say that in most cases both goals are mutually exclusive. Learning slowly and repeating something often, which takes time, helps to form a lasting memory.
What also helps is an intense emotional context. It does not matter so much whether the emotion is positive or negative. For example, if I had to solve a sever IT problem under time pressure, I might remember the details quite well. But when I worked calmly for weeks on an implementation, may it be simple or complex, I start to forget the details almost immediately after shifting to something else. However, I discovered that I might often quickly immerse myself back into it again at a later time.
There is also this phenomenon that I can reproduce in detail knowledge that I learned decades ago at school or university, but that I am not so good in reproducing what I implemented in the last couple of years. On the other side, I am nowadays a lot faster in adapting new things that are somehow related to my old knowledge, such as looking at a piece of code in an unfamiliar programming language and understand the algorithm.
What also helped a lot in creating a lasting memory was writing explanatory essays or tutorials. I mean not quick notes, but really intense thinking and optimization of the writing up to the point where it would even please your enemy.