doubt is the origin of wisdom.
“ If you would be a real seeker after  t r u t h 
it is necessary that
at least once in your life you  d o u b t
as far as possible
 a l l  things
When it is not in our power
to  d e t e r m i n e  what is true
we ought to follow what is most  p r o b a b l e
I suppose
therefore that
all things I see are illusions
I believe that nothing has ever existed
of everything my  l y i n g  memory tells me
I think I have no  s e n s e 
What is there then
that can be taken as  t r u e 
Perhaps only this one thing
that nothing at all is  c e r t a i n . ” 
- René Descartes
(Credits to marianista)