In Covid's case, wearing a mask only reduces the chance of you contracting the virus by 2%. The real reduction comes from the other person wearing a mask ~20% reduction).

Thus, you can't simply choose to keep wearing masks and get significant reductions in getting sick. Everyone would have to keep wearing masks, which is very unlikely.

Similarly, before the pandemic it was totally normal to go to parties with a cold or respiratory illness. I sincerely hope people keep the behavioral shift of not going to any events when sick, but humans are selfish and I bet they will largely return to their selfish ways