Actually my old textbooks are surprisingly clean and pretty much doodles free, except for my over zealous use of the highlighter on every other paragraph. My lecture notes on the other hand are full of doodles depending on how much I like the professor.
The real reason I don’t throw my textbooks away is because they do hold nice memories for me. Not so much for certain subjects like economics, business management. There were the first to go. But I do like topics like advertising, consumer behaviour and it is fun to take them out once in a long while and just flip through them. Likewise for my assignments, it is interesting to read what I wrote years back, sometimes just to have a good laugh.
Hopefully, my blog can last for a long time so that I can look back at it and say “I can’t believe I wrote all that?”