What’s the dumbest thing you’ve done or overlooked while working on a vehicle?

Surely everyone has done something really silly at one point or another..

I had an idle problem in my old Jeep, cleaned the throttle body, checked the air filter, smoke test, etc.. turned out the floor mat was on top of the gas pedal.

My brother had a dead petal in his mustang so he changed the clutch and all the associated parts. Turned out to be a cheap plastic clutch quadrant had stripped and the cable was slipping off the side of it.

Surely everyone has done something really silly at one point or another..

I had an idle problem in my old Jeep, cleaned the throttle body, checked the air filter, smoke test, etc.. turned out the floor mat was on top of the gas pedal.

My brother had a dead petal in his mustang so he changed the clutch and all the associated parts. Turned out to be a cheap plastic clutch quadrant had stripped and the cable was slipping off the side of it.