Then the girl in the shop I get most of my gear from showed me the scar on her head where a snowboarded nearly scalped her and that was it- bought one that day.
I have a unusually large head so getting a good fit hasn't always been easy but I find Giro have the right sizes. Have both bike and skiing helmets from them. Back in the day, the Protec XXL was the only Kayaking lid I could get to fit...