Lost your marbles?

  "Marblescape"

marbles
Slang - normal rational faculties; sanity; wits; common sense;

to have all one's marbles; to lose one's marbles

“Common sense is not so common.” 

- Voltaire

 

"The three great essentials to achieve anything worthwhile are,

 first, hard work; second, stick-to-itiveness; third, common sense.” 

-Thomas A. Edison