To attach a couple of personal anecdotes to this:
1) I once was in a position where I had root on the linux boxes at a large corporation because I had been a sysadmin there and even when I changed roles, I was never removed from sudoers. Years later there was an accusation that someone had stolen source code and taken it with them to a new job. On its face this made absolutely no sense whatsoever - the system they were accused of stealing was a complete pos in the middle of a complex ecosystem so even if you had it, you couldn’t use it without all the other pieces and in any case, it was old and outdated and just total garbage. Anyway this accusation was somewhat hush—hush so the cto came to me and asked me to just look into whether or not it could be true. Sure enough, there in his bash history I could see him checking out the code and pushing it to an external repo. It made absolutely no sense, but he had indeed stolen the source code to a system that was a total piece of junk. He ended up with a criminal conviction, he lost his shiny new job, his wife left him etc. It was very said and baffling.
2)Second example, fast forward some years and I was working for a saas provider. We had won an initial proof of concept and were negotiating a 5-year, multi-million dollar contract. At the same time, our client asked us to just do a free two-week spike on something unrelated. We had to sign a (different) zero dollar contract to cover licenses, liability etc for the free spike. The same purchasing lawyer was working on both contracts. The usual contracting process is you send the contract over to the other side with some markup and comments, they make some markup and comments, you propose language, they amend it, they propose language, you amend it, eventually everyone agrees and you make a clean copy and both sides sign. While we were doing this for the big contract, we got to the point of signing the zero dollar contract. At the last moment with everything agreed, the other side said they would make the clean copy. They sent it over to us and when we did our final check before signing we found the guy on the other side had meticulously gone through and made a version which accepted all their changes and backed out all of our changes. This required a lot of extra work and could not have been an accident (think cherrypicking commits and fixing all the merge conflicts using only MS Word revision history), and it was on the zero dollar contract so there was no conceivable upside except he could say he “won” somehow by tricking us. All this while we were negotiating the multi-million dollar multiyear contract. It made absolutely no sense whatsoever to do what he did. There is no way to understand why he decided to do it, but he did it.
So yeah, don’t even try to understand why some people do the unethical things they do. Scorpions gotta sting. It’s just what they do.