Was in a situation yesterday where i'm sure my helmet prevented myself getting hit by a car. 3 lanes of traffic had made a gap to allow a car turning left to pass through. I couldn't see him. By the time I rode into the gap and saw him, he slowed down in anticipation of me coming by. I was hidden behind the rows of cars, except my helmet was just above them. I believe that's how he was able to spot me.

A situation where you might regret not wearing a helmet is very possible.

"I shouldn't have worn a helmet" - No One Ever