When they do and come back into the ball, they reverse and it makes them open up, fall back, and lose power. True power can be explained as if the face of the club is a door. The face opens like a door and it closes like door. There may be no place where good tempo is more important than in a greenside sand trap. Yet there may be no place where anxiety and tension interfere more with good tempo than in that same bunker.
Most amateurs are deathly afraid of a shot from the sand, and that fear translates into tension.
The truth of the matter is that there is more margin for error in the sand than if you are hitting a pitch or chip shot from grass. In those situations you have to strike the ball precisely. In the sand, because you are not trying to strike the ball itself but the sand behind and underneath the ball, you can miss your shot with the clubhead by an inch or more and still get a satisfactory result. The single most valuable thought you can carry with you into a sand trap is to finish the swing. In the outings that I conduct and the pro-ams in which I play, I see too many players leave the club stuck in the sand.