I would read sidebars most of the time but sometimes I didn't understand the way the mods intended the rules to be understood. For example I posted a link to an on-topic podcast or blog post. But it gets taken down for being "self promotion" even though there is no reason to believe (or even allegation) that I had anything to do with the production. But since the mods have no way of telling apart sock puppets from legitimate third parties, they have banned all blogs and podcasts to be fair. Silly me I thought "self promotion" meant you were "promoting" your "self". But actually they just don't accept blogs, podcasts, youtubes etc.
Other times there are banned domains. Like one time I made a self post in a tech forum that mentioned an item on aliexpress. But aliexpress is banned because there was so much spam. Another time I linked to an image from pinterest in a hobby sub. Both taken down by automod.
Eventually you learn stuff like this although it requires a mod to take the time to tell you. It's annoying how the posts are silently hidden without notification or explanation. I got in the habit of checking posts with no/low comments in incognito. That's how you learn it was taken down but you then have to message the mods to learn why.