Relativity challenges your basic intuitions that you've built up from everyday experience. It says your experience of time is not what you think it is, that time is malleable. Your experience of space is not what you think it is; it can stretch and shrink.

No matter how hard you try to teach your cat general relativity, you're going to fail.

If a photon is emitted by an electron inside of a clock on Earth and it travels to a clock four light years away, time stops for the clock on Earth and time jumps forward eight years for the distant clock, also the electron that will capture the photon becomes infinitely large, relative to the photon but the electron that emitted it does not become infinitely small therefore, time is not perfectly symmetrical.

I'd say many features of string theory don't mesh with what we observe in everyday life.

Einstein gave us a problem he knew we would never solve.

The math of quantum mechanics and the math of general relativity, when they confront one another, they are ferocious antagonists and the equations don't work.