Top players not castling at all or waiting until the last possible moment to try to squeeze every possible resource out of the position has been the bane of my life for the last 5 years.
an early queen move
losing castling rights with ... Rg8
knight on the rim
not knowing that rooks are 5 worth points and bishops only 3
not taking the opportunity to castle long
too many pawn moves in (9 of his first 22)
putting his bishop on prise
letting his queen be pinned against his king
Frankly, young Master Kramnik would have earned himself a stern lecture in one of my beginners’ classes playing like that.