I forgot my mask after changing cars and going to get petrol. That maskless incident really got me out of the mask habit and now I don't bother unless I have one readily to hand.
Just read about masks giving a possible similar benefit to a vaccination.
If you catch CV through a mask it is very likely to be a low viral load ( unless you are in a hospital where the viral load is massive anyway ) - which generates an immune response similar to what a vaccine would...