When in doubt, tell the truth. That maxim I did invent, but never expected it to be applied to me. I did say, "When you are in doubt," but when I am in doubt myself I use more sagacity.
I am, and have been for years, a confirmed anti-vaccinationist...I have not the least doubt in my mind that vaccination is a filthy process that is harmful in the end.
A man was meant to be doubtful about himself, but undoubting about the truth; this has been reversed. Nowadays the part of a man that a man does assert is exactly the part he ought not to assert - himself. The part he doubts is exactly the part he ought not to doubt - the Divine Reason.
Given the millions of billions of Earth-like planets, life elsewhere in the Universe without a doubt, does exist. In the vastness of the Universe we are not alone.
In dealing with the arrogant asserter of doubt, it is not the right method to tell him to stop doubting. It is rather the right method to tell him to go on doubting, to doubt a little more, to doubt every day newer and wilder things in the universe, until at last, by some strange enlightenment, he may begin to doubt himself.