I married a guy like that too. He also had the belief that if he didn't say anything then it wasn't a lie...like when he didn't tell me about the letter from the IRS about owing back taxes. When I did find out about it he said he couldn't figure out the problem so he just ignored it. I was always cleaning up messes he made & never told me about....but I always found out (33 years I stayed married to that before I had enough & left)
He was diagnosed with adult ADD in his late 50's (obviously had it all along) but what they never added to it because it was newer ex at the time was high functioning ASD.
He was constantly full of excuses as to why he couldn't do things that basically normal minds could figure out. We were both computer engineers & he was always giving excuses for things in his career that a wife that wasn't in the same career might buy into but I knew better & didn't let it slide. Constant conflict the whole marriage.
After I left I realized that he was incapable of taking responsibility for what he did....maybe because the way his mind worked he didn't even comprehend the problems. Not sure the lies were even actually intentional.....then I caught them & that was when lies turned into excuses & it started getting worse the older he got.
There are so many reasons people lie & make lies into excuses for things. Sometimes I think my now EX- husband really couldn't handle a wife that was just as capable (if not more) & the lies & cover-ups were because he didn't want to look like an incompetent husband.