How many blades does your razor have?
First, there was the single blade cut throat razor. Many people hurt themselves.
Then came the single bladed 'safety razor'. Many people had razor burn.
Then came the two bladed razor. Many people used these for many years.
Then came the three bladed razor. It was billed as being 50% better, but many people ignored it.
Then came the four bladed razor. Even less people thought it was a good idea.
At last, there's a five bladed razor, because apparently four blades can cause irritation.
It's not the number of blades that cause irritation - it's the advertising treadmill.
Update: Dan wrote in with a link to an Onion article - priceless!