go-to move?

it's the thing the kid is most comfortable doing, and is being advised not to do it every time.

in basketball, a "go-to move" is an oft-practiced move a player is confident he can make with the clock winding down in a must-win game...

"go-to" is a relatively new idiom that means reliable or best option.

So you can have a go-to person or place.

Mary is the go-to person for info on sewing.

Fred's Diner is the go-to place for good fish.

In your example, the person is told not to make a certain movement his "go-to" move. He should hold back and use it as a special skill movement.