Your assumptions are your windows on the world. Scrub them off every once in a while, or the light won't come in.
We now have a whole culture based on the assumption that people know nothing and so anything can be said to them.
You must stick to your conviction, but be ready to abandon your assumptions.
When speculation has done its worst, two and two still make four.
The temptation to form premature theories upon insufficient data is the bane of our profession.
Theories are always very thin and insubstantial, experience only is tangible.
A speculator is a man who observes the future, and acts before it occurs.
It is theory that decides what can be observed.
There are two times in a man's life when he should not speculate: when he can't afford it, and when he can.
One must credit an hypothesis with all that has had to be discovered in order to demolish it.