Clarke's First Law:

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.

Clarke's Second Law:

The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

Clarke's Third Law:

Any sufficiently advanced technology is indistinguishable from magic.

Corollary to Clarke's Third Law:

Any technology distinguishable from magic is insufficiently advanced.

For more information about the man behind these quotes, see Arthur C. Clarke.