[ 8/5/20 ]
As several others here have noted – absolute certainty is not possible – for many different sets of reasons.
One simple idea is that most numbers cannot be known with absolute accuracy – like the number Pi. Pi may be calculated forever, without reaching any definite and certain end. Most calculations to do with circles or periodic activity require the use of Pi, so must necessarily contain some degree of uncertainty. There is a mathematical proof that there are more numbers like Pi that cannot be known than there are numbers like integers and fractions that can.
Then there are classes of systems that cannot be predicted even in theory, things like maximal computational complexity, halting problems, etc.
Then there are many levels of measurement error. All technologies that actually measure things are subject to multiple classes of error.
Then there is fundamental quantum uncertainty – like Heisenberg uncertainty.
Then there is fundamental logical uncertainty – like Goedel incompleteness.
Then there is just the sheer numeric complexity of reality. It is really worth spending a few hours working through the numbers of just how many atoms there are in each of us and how often they interact with each other, and how much uncertainty is necessarily present in every one of those interactions.
Uncertainty is fundamental to existence, and is an essential aspect of every level of life. Evolution is based on it in a very real sense.
The idea of absolute certainty is an illusion that some hold on to that comes from the very low resolution models of reality that children must necessarily start with.
Time to upgrade your model, to enable it to deal with the uncertainty that is (beyond any shadow of reasonable doubt) fundamental to the reality we exist in.