Our perceptions are fallible. We sometimes see what isn't there. We are prey to optical illusions. Occasionally we hallucinate. We are error-prone.
Carl SaganAn atheist is someone who is certain that God does not exist, someone who has compelling evidence against the existence of God. I know of no such compelling evidence. Because God can be relegated to remote times and places and to ultimate causes, we would have to know a great deal more about the universe than we do now to be sure that no such God exists. To be certain of the existence of God and to be certain of the nonexistence of God seem to me to be the confident extremes in a subject so riddled with doubt and uncertainty as to inspire very little confidence indeed.
Carl SaganPerhaps, in retrospect, there would be little motivation even for malevolent extraterrestrials to attack the Earth; perhaps, after a preliminary survey, they might decide it is more expedient just to be patient for a little while and wait for us to self-destruct.
Carl SaganIf we continue to accumulate only power and not wisdom, we will surely destroy ourselves.
Carl SaganWhat is called for is an exquisite balance between two conflicting needs: the most skeptical scrutiny of all hypotheses that are served up to us and at the same time a great openness to new ideas. If you are only skeptical, then no new ideas make it through to you. On the other hand, if you are open to the point of gullibility and have not an ounce of skeptical sense in you, then you cannot distinguish useful ideas from the worthless ones.
Carl Sagan