Learn to accept that sometimes you just not gonna get something, at least at this particular place and time.
You have a lot of things ahead to research - manage your time. Don’t spend much time on one particular problem.
If you fell like you don’t understand something yet, it’s ok. Let it go, move on. Apply black box method to unknown yet things.
Often the solution comes when the mind is at rest:
Лучший отдых - это смена деятельности.