It's always been pretty hard to accidentally unfollow someone on Instagram (even though you've probably used that excuse on occasion). Unfollowing someone requires a two-step process. First, click the half person symbol with a check next to it, indicating you follow that person. Then a message pops up that reads, "If you change your mind, you'll have to request to follow (insert name) again," along with an Unfollow button.
Well, Instagram just made unfollowing someone a one-step process, making your "It was an accident" excuse a lot more believable. Now when you click Unfollow, you actually unfollow that person immediately, with no opportunity to change your mind. You then have the option to follow back, but the person will know you've unfollowed. And do you really need that kind of drama in your life? Better to just be careful with your clicky fingers.
The update hasn't rolled out to all user accounts, but expect it to soon.