About 90 years ago, just after the great revolutions of relativity and quantum mechanics, H. Weyl and W. Pauli expressed serious concerns about the possibility of constructing a truly unified theory of space, time, and matter. I will give my personal view on the status of this issue in the light of the successes and puzzles of our present ``Standard Model of Nature'' and of some 40 years of exciting/frustrating work in string theory.