William James

Lost epiphanies create regret.  Here's an anecdote...and an answer.

After many failed attempts to recollect his deep understanding of the ultimate unity of all things,  James tied a pen to his hand during his next brain quest.  

As expected he had a brilliant revelation and this time he wrote it down.

Hours later, he read the philosophical idea that poured from his subconscious:

"Everything has a petroleumlike smell."