"Don't cross the streams!"

[WillieL]

I keep this one on top of my tool cabinet to serve as a constant reminder. 

I wanted to clean up the side of a piece of aluminium bar stock in the vice on my mill. I normally reach up to turn the mill on with my left hand being that the switch is on the left side of the head. I got ahead of myself and started working the left hand crank on the table in order to touch off the cutter to the bar stock. I realized the cutter wasn't turning and reached up with my right hand to start the spindle.
As the 2 flute end mill lightly touched the side of the stock I heard a quick "tink" sound but no cutting sounds. I looked to see the bottom half of my mill cutter laying on the machine table. 

After a lot of head scratching and trying to "re-create the crime scene" it finally occurred to me that since I switched hands when reaching for the ON switch, my brain subconsciously told me to reverse the movement of my hand as well... resulting in me switching the spindle on in REVERSE.
 

[Pete.]

A well known phenomenon. Try his:

Tape a piece of paper to the wall. Now stand on one foot and make clockwise circles with your raised foot. Whilst doing that, draw a big 6 on the paper - your foot will switch to making circles anti-clockwise.

[WillieL]

Yes I have tried that before, and it's true. In reality I just blame it on good old fashioned 'not paying attention' to what I was doing. The sad thing is - one of the first things I did after buying the mill was to make a label for the switch to make sure things like that would not happen.