Only as you do know yourself can your brain serve you as a sharp and efficient tool. Know your failings, passions, and prejudices so you can separate them from what you see. Know also when you actually have thought through to the nature of the thing with which you are dealing and when you are not thinking at all.
A rational process is a moral process. You may make an error at any step of it, with nothing to protect you but your own severity, or you may try to cheat, to fake the evidence and evade the effort of the quest - but if devotion to the truth is the hallmark of morality, then there is no greater, nobler, more heroic form of devotion than the act of a man who assumes the responsibility of thinking.
You who prattle that morality is social and that man would need no morality on a desert island - it is on a desert island that he would need it most. Let him try to claim, when there are no victims to pay for it, that a rock is a house, that sand is clothing, that food will drop into his mouth without cause or effort, that he will collect a harvest tomorrow by devouring his stock seed today - and reality will wipe him out, as he deserves; reality will show him that life is a value to be bought and that thinking is the only coin noble enough to buy it.
No matter how vast your knowledge or how modest, it is your own mind that has to acquire it. It is only with your own knowledge that you can deal. It is only your own knowledge that you can claim to possess or ask others to consider. Your mind is your only judge of truth - and if others dissent from your verdict, reality is the court of final appeal. Nothing but a man's mind can perform that complex, delicate, crucial process of identification which is thinking. Nothing can direct the process but his own judgment. Nothing can direct his judgment but his moral integrity.
Honesty is the recognition of the fact that the unreal is unreal and can have no value, that neither love nor fame nor cash is a value if obtained by fraud - that an attempt to gain a value by deceiving the mind of others is an act of raising your victims to a position higher than reality, where you become a pawn of their blindness, a slave of their non-thinking and their evasions, while their intelligence, their rationality, their perceptiveness become the enemies you have to dread and flee - that you do not care to live as a dependent, least of all a dependent on the stupidity of others, or as a fool whose source of values is the fools he succeeds in fooling - that honesty is not a social duty, not a sacrifice for the sake of others, but the most profoundly selfish virtue man can practice: his refusal to sacrifice the reality of his own existence to the deluded consciousness of others.
Faith gives the courage to live and do. Scientists, with their disciplined thinking, like others, need a basis for the good life, for aspiration, for courage to do great deeds. They need a faith to live by. The hope of the world lies in those who have such faith and who use the methods of science to make their visions become real. Visions and hope and faith are not part of science. They are beyond the nature that science knows. Of such is the religion that gives meaning to life.