If you're not fitted and trained on the PPE you're using, it's more likely to cause harm than to provide any protection. If not direct harm, then by providing a false sense of security.

You need to not only know how to use PPE, but know what it's limitations are, and what it's designed to actually protect you from.

Wearing a shield thinking it provides any protection from an aerosolized virus is a perfect example of having the wrong expectations from a piece of equipment.