What part of this don't you understand? If two blades is good, and three blades is better, obviously five blades would make us the best fucking razor that ever existed. Comprende? We didn't claw our way to the top of the razor game by clinging to the two-blade industry standard. We got here by taking chances. Well, five blades is the biggest chance of all.
Here's the report from Engineering. Someone put it in the bathroom: I want to wipe my ass with it. They don't tell me what to invent—I tell them. And I'm telling them to stick two more blades in there. I don't care how. Make the blades so thin they're invisible. Put some on the handle. I don't care if they have to cram the fifth blade in perpendicular to the other four, just do it!
The 5-blade razor has been out awhile, but I thought this "editorial" summed up its origins nicely.