In his last couple of interviews LW did mention quite specifically individual mistakes and how he couldn't stop them happening because of players concentration levels. I fully understand the concentration thing, the players he refers to are L2 (and probably more comfortable at NL), very aware of results hinging on their performance and desperate to not make an error. Bit of a vicious circle for some of them, try like hell, panic, brain fart, mistake. None of them are bad people and are giving all they can but they just aren't up to it I'm afraid.