Sometimes learning happens more easily than other times, and it's useful to understand why. There are many factors involved, and one is the regularity with which you think about the topic that you're learning.
Learning is essentially the process of forming sufficient links in the brain between related ideas, and so while learning anything complex it's important to be able to hold a large amount of information in memory ready for processing.
Our short-term memory is limited, so for complex tasks it's essential to use medium and longer-term memory to assist with the learning process. Think how an expert in anything improves - whether it's a professional tennis player, a musician or a businessman: each refinement in their skill is based on lots of previous experience, mostly held in longer-term memory.
Information gets placed into medium/longer-term memory when there are enough neural connections that involve it. This sometimes happens by random chance, but usually it requires deliberate repetition. It also fades from there quite quickly without rehearsal (which would link it to other information).
The implication of this is that if you are trying to learn a skill by occasional practice (rather than frequent practice) then rather than slow progress, you may find that you make almost no progress at all. You never have enough information stored in medium-term memory to make meaningful progress, because much of it evaporates between successive practices. You need to keep up the momentum when learning in order to make meaningful progress.