It's similar to reading code in a boilerplate-heavy language. It's hard at first, but once you've read a few, your brain learns to filter out the chaff and get to the juicy bits. I'm not a legal expert at all and I don't expect to detect intentionally tricky language or other such traps, but even a 20% understanding of these can get you 80% of the value, in learning how broad the rights they give themselves are, how much they're willing to commit to restrictions on themselves (regarding your data, etc.), and maybe learn a thing or two about how the legal system works, too.
You never remember what happened or who said what but you'll always remember how they make you feel. There are companies and personalities that I just refuse to have anything to do with, decades after the fact.
I know... I should.. but urgh..
Funny video of Michael McIntyre talking about this very thing: https://www.youtube.com/watch?v=O5FeZti1cjs