You lose the thread of your argument.
I get fidgety, lose the thread, begin looking for something else to do.
Now my concentration often starts to drift after two or three pages. I get fidgety, lose the thread, begin looking for something else to do.
If someone enters the room while one is watching television — a friend, a relative, a child, someone, perhaps, one has not seen for some time — one must continue to watch or one will lose the thread.
