It's just weird

I don't know why. But since the past week, my shoelace tends to untie itself a few times a day. It's just weird cause I've been tying it the same for the past 4 years. So now I have to tie them up like 4 or 5 times a day. That's both sides. I tried other methods of tie-ing them, though still the same. Maybe it has something to do with the shoelace... or is it something else?