This is a human factors issue and is rare but it does occasionally happen and can happen with an experienced or inexperienced pilot. Back in the 80's as a two striper on a 747 classic I called "positive climb" and the Captain with 28 years in the company called "flap up". I replied "gear up" paused, he confirmed and I raised the gear. Later the Captain could not believe he had said flap but fortunately the Flight Engineer told him in no uncertain terms he had.
Loganair back in the 80's had a policy of hitting flap up on touchdown on the Fokker F27 to dump lift and get the weight on the wheels. Unfortunately on one touchdown the copilot selected the gear up and sod's law it was a crosswind and the squat switch was on the downwind main gear and the gear raised dinging both props.
Occasionally you get a pilot calling for gear up and the other pilot's hand goes towards the flap lever momentarily before self correcting. Seen it all but it is very rare that someone goes ahead and actually selects flap up instead of gear up. The beauty of having two pilots is one notices the error and normally stops it before it happens. But if an error can be made it will be made due fatigue, complacency, distraction.