For some reason there are a lot of people who can't close one eye when looking through a binocular. To compensate for this I've seen folks try all kinds of things, but most often they hold a hand over one objective lens of their binocular while trying to focus with the other hand. This doesn't work so well as you end up mashing the bino into your face.
A better way is to take a lens cap and cover up the objective lens of the side you don't want to look through. Don't spread this around, though, because it is lots of fun watching people struggle trying it the other way.