I went to my optometrist this morning. They don't require customers to mask anymore, but were happy to have all their staff wear masks, including receptionists.

After my appointment finished, I noticed that all the waiting patients had masks as well, which I originally thought was just good luck. However, the receptionist told me that every customer had entered without a mask, and within a few minutes they all either put on their own mask or asked for one from the receptionist, noticing that they were the odd one out.

This experience powerfully showed me that for many, the decision to mask or not is heavily influenced by peer pressure.