If the problem is too hard it's not always possible to talk or draw something while thinking about it. You go through dozens of possible solutions in your head,

If the problem is too hard it's not always possible to talk or draw something while thinking about it. You go through dozens of possible solutions in your head, to find a good one. That's like asking a champion chessplayer to explain what he's thinking about while trying to make a move. So this only works if the candidate already knows the solution, and knows which way is right and just explains that one (and maybe a few bad alternatives on purpose). Or if the problem is relatively easy.