When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
Arthur C. Clarke
PhD Comics has an interesting video online. The part in the beginning (“We didn’t know it was impossible.”) reminded me of the quotation above. 😉
As necessary as it is to be in the community and know the literature, there is a danger with being (or considering oneself) an expert. After all, if might have been impossible at the time, but the basis of knowledge improves and so do our methods/technology.