All thought is a feat of association; having what's in front of you bring up something in your mind that you almost didn't know you knew.
Robert Frost
To him whose elastic and vigorous thought keeps pace with the sun, the day is a perpetual morning.
Henry David Thoreau
We find it hard to believe that other people's thoughts are as silly as our own, but they probably are.
Jams Harvey Robinson
The thoughts that come often unsought, and, as it were, drop into the mind, are commonly the most valuable of any we have.
John Locke
The happiest people in this world are those who have the most interesting thoughts
William Lyon Phelps
Our brains are fairly powerful, but our conscious minds are still extremely limited in their ability to hold onto multiple simultaneous thoughts
Steve Pavlina