Did you know that while HEPA filters might remove well over 99% of air particulates once that's done you've still got 100% of the remaining particulates in the air?
Did you know that if I steal half of your money you've still got 100% of your remaining money?
I believe its common to just give up a fight like this because it's really never over, and no single step leads directly to perfection. Why recycle when some recycling still ends up in a landfill in India ? Why help a homeless person when there still will be homeless tomorrow?
OTOH, most of us are still getting up every morning and go to work.
100% can be split in so many small sums. Each percent is worth taking.