Attention wanders off in the middle of the good thing. That is simply what it does. The trick is not stopping it but keeping something small back in view — the heat of a mug through both palms, the fact that the room is warm, someone in the next room laughing at their phone.
Ten seconds is enough. Not as a distraction from what is difficult, but because the difficult thing has had your attention all day and something else is owed a turn.