There is no absolute here. While I agree that a great degree of understanding is desirable, lots of concepts and techniques don’t sink in until hours, days or even years after being presented.

I still remember powering through lots problems without much clarity and achieving the right answer. Every attempt, failed or successful, got me closer to really understand what I was doing.

It’s ok not to understand a topic the first or nth-time time you come across it. If you follow through, something will stick, and sooner than later you’ll get a good enough picture.

They are like seeds, you know.