Ever wondered what those weird extra shoelace holes on your sneakers are for?

Turns out they actually serve a brilliant purpose.

A YouTube video that’s gone viral this week shows how those mysterious extra holes can actually help you fit your shoes better, and thus prevent blisters.

The method is known as a “heel lock” or “lace lock”, and it creates extra friction between the laces at your ankles, keeping the ankle and heel areas snug.

So far, the video has been viewed millions of times.

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