String theory is all mathematics and unprovable propositions so why shoukd we place our faith in it?
For one, mathematics has served us well, with no animony. It describes the universe well, with no inconsistency.
Secondly, there doesn't seem to be a better alternate theory - none. Reconciling the macro (General Theory of Ralativity) and Quantum Physics necessitates strings, how gravity behaves between the two theories only makes sense with sting theory. No other theory suffices. Excuse the pun but strings tie up everything in a not-so-neat bunde but there you have it.
Yet you are who you are despite all your particles zipping off into infinite flux. Somehow, the you that you are maintains some stability, conisistent instanteation of the You that you are. We don't just wiggle around as two-dimensional objects on a screen but just who we are. And yet, everything that is you is a particle, wave, whatever, squiggling into the ether and other dimensions, slipfinny and elusive, the slippery and undefinable You zigging and zagging elsewheres and at the same time here. So what's to say you even exist?
Because there You are.
Nothing really explains that or even quantifies that; not You, your essence. Nothing can. Yes, we can explain how everything within You works but we're clueless as to that which makes you You.
Take comfort in that lack of knowledge.