Some authors write in a super dry way and have no idea how to transmit what they know in an exciting way.
They will overlaod you with irrelevant information and flood you with detailed facts without giving your structure or the full picture.
If you take notes, rather than simply writing one fact after the other, put the name of the topic in the centre and from that center radiate facts out.
Ad colours to highlight what really matters.
Use short concepts rather tha full explanatory sentences.
This is what will digest any topic for you!