Have you ever stared at those extra shoelace holes in your running shoes and thought, “What in the world are these for?!”

You can now wonder no more.

According to an eye-opening YouTube video that’s gone viral this week, those extra holes can actually serve an important purpose. They can help make shoes fit better, and thus prevent blisters.

The trick is to create what’s known as a “heel lock” or “lace lock” with the extra holes. This method is said to create extra friction between the laces at your ankle, thus keeping the ankle and heel area nice and snug.

Just remember not to tie your laces too tightly.