The mind that engages in subjects of too great variety becomes confused and weakened.

I believe man will fly and I base this assumption on the fact that God has blessed us with minds that are capable of imagining it. Anything that can be dreamt of will eventually be built. Anyone who says otherwise is a fool.
(As quoted by a fictional Leonardo in DaVinci Demons)

As iron rusts when not used, and water gets foul from standing or turns to ice when exposed to cold, so the intellect degenerates without exercise.
-Leonard Da Vinci