Bertrand Russell's grandmother tried to find absolute certainty in religion and Russell tried to find it in mathematics, but mathematics and religion (and philosophy and language) are products of the human mind. They are attempts to create a map or model of reality, but models and maps are by their nature simplifications. They can never be exact replicas of reality; as Alfred Korzybski put it "the map is not the territory".
The authors portray Russell's quest for mathematical certainty as a "spiritual tragedy" because it was ultimately unsuccessful, but by the same standards John Milton's Paradise Lost is unsuccessful because it did not achieve the author's stated goal of justifying the ways of God to man. Paradise Lost is still the greatest poem in the English language and Russell's work in mathematics paved the way for Alan Turing and John von Neumann and the invention of the computer. I would not call that a tragedy by any reasonable measure.