I often feel like giving up. I often falter. But I always come back to everything I truly believe in.
I do quit specific things, sometimes. So if a relationship becomes completely toxic and destructive, I will end it. If I find someone has become criminal or deeply harmful, I will stop supporting that person. So, I may change tactics and I watch - often sadly - as my team changes, but I do not give up.
I admire ChitrangadaSharan's answer, and I sympathize with ResearchPapers. We are not strong enough never to fall down. But we are strong enough to get up again, and again. And all we have to do, in the moment, is get up after we fall down.