It's less of a problem of focusing my brain and more of a problem of unfocusing it. The game is fun for me for ~3 hours, then I start to lose focus, and then look up at the clock and realize that the day is gone. In the meanwhile, I LOVE it when I can see a long word with a few letters in it and recognize the patterns of the letters that are still missing.
(A few years ago I sat down to improve my minesweeper times. I looked back up at the clock and five hours had gone by.)