Progression in the Unknown
When you start exploring new and unknown fields; even with all the time you need, it could be harder than you think to keep focus (and sane).
Because rapidly, basic knowledge of other fields are needed to keep moving forward, and you have to stop your progression in order to learn them. In fact, in the beginning, you are moving very slowly. So doubts are starting to emerge… and kill your motivation. You will keep this feeling for yourself because you have nothing to show (yet).
When I started game development, I often felt depressed after hours trying to draw some triangles on the screen. Even after that, I struggled with understanding transformation matrices, collision equations… And I wasn’t particularly "good" at math when I was younger… so now trying to really understand all those were kind of odd.
But with a bit of patience and time, it gets better. You will build intuition, you will finally understand things you couldn’t before, and above all, you will deeply trust yourself about learning new things.
You will feel invincible.