I follow the camp that says tension is the culprit. I just recently
did a renter's check ride in a 172 at Camarillo, CA (CMA). The check pilot
(a CFI) had me do 3 T&Gs, in addition to the other stuff. They were okay,
but just okay. My personal gauge said they were not very good landings.
Later on in the day, I absolutely greased four in a row.... with the right
seat empty. I really think it had to do with trying too hard. Forcing the
skill, so to speak.