As the popular phrase has it:
"Assume makes an ass of u and me"
Or does it?
Well I suppose it does, provided that either (a) you don't know the meaning of the word "assume" or (b) you haven't been taught how to assume.
An assumption is not a guess. It is a reasoned or justified statement of some fact that you think is true, AND WHICH you expect to be confirmed or denied before you proceed. The saying ought really to be:
"Acting on what you assume prior to receiving confirmation, makes an ass of u and me."
There are three distinct levels of certainty that seem very seldom to be properly used, and even less often properly understood when they are used correctly:
assume indicates a proposal or question that needs to be confirmed , OR is an explanation for other choices made.
presume indicates that I have some concrete reason for believing something to be fact
expect indicates that I am sure that something will happen
"Arriving at a signpost with a picture of a bus on it, I assumed it was a bus stop and began to wait."
I may be right or wrong.
"I presumed the bus that I saw arriving would stop at the bus stop."
If my first assumption is right, then it is reasonable of me to think that the bus that I saw would stop. Of course, if my assumption was wrong...
"I expected to be allowed on the bus."
By this time the bus has stopped, it's going where I want to go, there's room aboard, and I have money to buy a ticket. I have every reason to think that I will be allowed on.
While expectation is not certainty, it is an honest substitute for it in situations that are too complex for certainty.
"I'm certain that if I drop this rock, it will fall to the ground."