It can happen easily. You drop a blade, get it sharpened or try to get hair out from behind the cutter and the alignment is off. The cutter is crooked and you HAVE to fix it. If you don't, you will get lines., tracking because it is now an injury risk as well.
I have a short video clip on how to adjust blades when this happens. AND I show you how using the MAC blade cleaning tool can prevent it from happening in the first place (from cleaning at least).