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.
It's murder to doubt yourself in life. It took until I was 45 to get to that point. As hard as it is in your work, it's harder in your life. But it can be done.
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.