Don't imagine that you'll discover {the truth} by accumulating more knowledge. Knowledge creates doubt, and doubt makes you ravenous for more knowledge. You can't get full eating this way.
Doubt, indulged and cherished, is in danger of becoming denial; but if honest, and bent on thorough investigation, it may soon lead to full establishment of the truth.
I believe that the starting point of faith is some doubt, not bein' so full of yourself and so confident that you are right and that God speaks only to us and doesn't speak to others, that God only cares about us and doesn't care about others.
Satisfy yourself beyond all doubt that you are qualified for the course to which you now aspire.....and try to achieve something in your own land before you venture on a strange one.
Everyone who observes himself doubting observes a truth, and about that which he observes he is certain; therefore he is certain about a truth. Everyone therefore who doubts whether truth exists has in himself a truth on which not to doubt.... Hence one who can doubt at all ought not to doubt the existence of truth.
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.
you must be careful never to allow doubt to paralyze you. always take the decisions you need to take, even if you're not sure you're doing the right thing. You'll never go wrong if, when you make a decision, you keep in mind an old German proverb: 'The devil is in the detail.' Remember that proverb and you'll always be able to turn a wrong decision into a right one.
There is nothing makes a man suspect much, more than to know little, and therefore men should remedy suspicion by procuring to know more, and not keep their suspicions in smother.