Simply put because I'm stubborn.
I refuse to give in or up on things, the harder something is the more I dig my heels in.
Whenever I'm having a hard time and it feels like the best option would be to just let go, give up the fight and accept that it - whatever it is - can't be done or achieved ...I snarl, frown and swear before just get on with it and attack the problematic thing even harder.
Yes I really do snarl that wasn't a typo.