I would add that the interested reader can go straight to Keynes’ important 1937 article where he emphasised the concept of uncertainty and its implications for economics:
Keynes, “The General Theory of Employment,” Quarterly Journal of Economics 51 (1937): 209–223.The crucial passage is here:
“By ‘uncertain’ knowledge, let me explain, I do not mean merely to distinguish what is known for certain from what is only probable. The game of roulette is not subject, in this sense, to uncertainty; nor is the prospect of a Victory bond being drawn. Or, again, the expectation of life is only slightly uncertain. Even the weather is only moderately uncertain. The sense in which I am using the term is that in which the prospect of a European war is uncertain, or the price of copper and the rate of interest twenty years hence, or the obsolescence of a new invention, or the position of private wealthowners in the social system in 1970. About these matters there is no scientific basis on which to form any calculable probability whatever” (Keynes 1937: 213–214).