What do you believe is true even though you cannot prove it?

Here is the link to a site that poses this question.
cf:
“He that will believe only what he can fully comprehend must have a long head or a very short creed.” — Teilhard de Chardin
“Shall I refuse my dinner because I do not fully understand the process of digestion?” — Oliver Heaviside
“It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence.” — William Kingdon Clifford
keywords: belief, ideas, speculation