Answer

To understand this, you first have to understand what a proof is. A proof is the derivation of a conclusion from premises. Therefore, the certainty of a conclusion can be no greater than the degree of certainty in the premises. See my article in Tzohar about Abraham our Patriarch and his hat, and in my book Two Carts.
Those files are intended to come out as a book, so at the moment I am unable to share them. I am still considering whether to upload them to the site in some form. You can keep following.
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Questioner:
And are there no certain premises? The very fact that I am alive? 1+1=2?
And besides that—where does the definite claim come from that there is no absolute certainty?
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Rabbi:
Who said that this is a certain claim?
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Questioner:
So you’re not certain that there is no absolute certainty, but only certain to a high degree of probability?
And what exactly is meant by saying that there isn’t
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Rabbi:
Indeed, I am not certain that there is no certainty. What do you mean, what is meant by it? If you don’t understand, then what have we been talking about until now?!
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Questioner:
I simply didn’t understand that specific sentence. What is the problem with proving things from certain premises?
And still—you are certain in your uncertainty about whether there is certainty or not.
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Rabbi:
No. We can keep going like this forever, but I don’t see what benefit there is in it.
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Questioner:
Isn’t your very existence a certain premise?
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Rabbi:
I am very convinced that I exist, but conviction is not certainty. Descartes, in his cogito argument, claimed that this is certain. I (like many others, greater than I) tend to think not, but it is hard for me to elaborate here (why it is not necessary).