Cutting a blind keyway

[Pete O]

Something I read that made sense was that the force acting on the cutter as it cuts into the leading edge of the slot, i.e. the direction of feed, causes it to flex to the side. This is apparently one more reason that a 2-flute cutter is better for slotting than, say, a four-flute cutter. Apart from the fact that a 2-flute cutter is more inherently rigid.
I read that on the internet 2 days ago so now I'm some kind of expert.