When you find yourself deep in the grind (and we all do and more often at the moment) there are only two choices:
Tough it out and get to the other side.
Give up what you’re doing (whatever that might be).
Both of these are entirely valid options and in the right circumstances each is the correct route to take.
The trick is not to be a grinder or a quitter, the trick is to have the insight to knowing which decision is correct in the right circumstances.
Many of the people whom you look up to, who have done great things and made it through the grind, will have had extraordinary stamina on some occasions and incredible insight into knowing when to stop when things weren’t working.
Working on a combination of stamina and judgement might be a better strategy than just building your muscles.