If you concentrate on sleep, the awareness of sleeplessness inhibits the relaxation and release necessary to fall asleep. If you take your focus off of the qualities needed to fall asleep and concentrate on staying awake, you'll tend to nod off.

It's almost as though thought processes must be "taken offline" in order to be examined. Bringing the process into awareness interferes with its functioning.

Worrying about happiness tends to be incompatible with happiness.