re: How much can bad science in Sci-Fi break immersion?

In Inception, they never really explain how the shared dreaming device work. You have to accept that shared dreaming is a thing and it works in order to enjoy the movie.

Also, this isn't from sci-fi, but this line from The Shawshank Redemption always irked me. "Five hundred yards. That's the length of five football fields, just shy of half a mile."