You can only know your thoughts about a subject if you are able to properly articulate them. If you are lacking that ability when conversing with others, more study is required. The standard is set. Being able to understand and explain go hand-in-hand.
We delude ourselves into thinking that we understand complex topics when, in fact, we do not.
What is the litmus test for such things? The answer is simple. Can you explain the concept to others? If not, you have more work to do. Articulation forces the point.
The Feynman technique advices one to be able to teach the subject to a five-year-old. If that is achieved, understanding has been successful.
That’s the gauge.