Yeah, nobody can explain it so we understand. I got an easy way. To oxidize is to bind oxygen with (something). See a famous example: carbon dioxide. It's the stuff we expel when we exhale. See another famous example: rust.

The term "oxidative" means it can easily bind to oxygen. This should give us a hint as to what should normally happen - it should bind to oxygen, but it doesn't, cuz there ain't any, so it binds to other stuff and that's a bad thing. If there was oxygen, it wouldn't be bad, cuz that's what oxygen is for - to bind to stuff in a normal way. We got lungs, see?

I wanted to say "but we don't rust, we metabolize", but then I read what "metabolize" means, and I decided that "to rust" is exactly what we do, and that's how we extract energy from the oxygen we breathe. Imagine if we were adapted to breathe hydrogen instead, then we'd hydrogenate, not oxidize, ya?

Anyways, the whole idea about oxidative stress leads us to conclude that oxygen is a bad guy, but we only need to hold our breath for a minute or two to realize the obvious BS. If there was a bad guy to blame, oxygen ain't it, there must be some other guy doing the deed in some different way. Let's see. We go low-carb, then everything improves. Well, we go high-carb, then everything goes worse. Must be the carbs. So, the stuff we blame on oxygen, I think we should blame it on glucose and other -oses instead.

Think of it this way. We got thousands of mitochondria for the unique purpose of oxidation, but only one cell nucleus where fermentation occurs. Without oxygen, it's fermentation, therefore any condition that reduces oxygen supply must be blamed on that, not on oxygen. I even think that there's so many mitochondria precisely for the purpose of taking care of the fermentation by-products cuz they're really bad for an oxidative organism. Do some HIIT, mitochondria increases in number, everything gets better (Hm, that's what happens too when we go low-carb, I wonder). Oxygen = good.