The Intelligent are Full of Doubt?

Today I share with you the following quotes: 

I must study politics and war that my sons may have liberty to study mathematics and philosophy. My sons ought to study mathematics and philosophy, geography, natural history, naval architecture, navigation, commerce, and agriculture, in order to give their children a right to study painting, poetry, music, architecture, statuary, tapestry, and porcelain.

...... John Adams(1735 - 1826), US former president

In the modern world the stupid are cocksure while the intelligent are full of doubt.

...... Bertrand Russell(1872-1970), British philosopher