Some think creating your own material based on what you want to learn may activate your semantic memory, which is the general world knowledge that we have accumulated throughout our lives, such as facts, ideas, and concepts.

Short simple read on why active learning is preferable to passive learning. Simply writing a sentence or two after you read something, generally makes the content more sticky, forming unbounded connections. Just like I did here!

That is why I believe the comments portion is Readup's most underrated feature.