Why is Sun in 8th bad if Sun is a “cruel” planet ?

It doesn’t really make sense to me tbh
Say Saturn in 6 is good he shrinks the issues, then by this logic Sun is supposed to burn the 8th house issues
Actually many rules don’t make any sense to me
I feel like it is supposed to be more intuitive and based on legends about the planets
Rather than textbooks
I feel like we misunderstand everything now