An expert is a person who has a very good reason for guessing wrong.

It's amazing how opinionated we can become concerning issues about which we know little, or even nothing at all. 

An expert is a person who has made all the mistakes that can be made in a very narrow field. ~ Bohr

An honest expert is also not afraid to say when they don't know or when they don't understand something, and is happy to be enlightened. ~ greythumb

Beware of the advice of experts.

It’s a lot easier to do something with the help of someone who has done the same thing many times.

Real experts aren't afraid to correct themselves or admit when they are wrong. ~ greythumb

What is required to be an expert is often a matter of great debate.