P.S.
Sometimes I think people don't realize how much a good or bad script can shape our perception of what chemistry is. There's a reason why actors and actresses thank the directors, producers, etc. whenever they receive awards. Their talent alone is not enough.
You know, Keira Knightley once said that, "Whether a film has worked or not, it's out of my hands. The only experience that I have is the actual making of it. After that, it's not mine. It's the director's, it's the editor's and then it's whether it captures the audience's imagination or not. "
And when asked about chemistry, here's what she had to say:
"Sometimes you can have great actors working together and yet something just slightly misses, so I guess if everybody has a common vision of what it is, if that's in sync, then that's what the chemistry is, not necessarily between the actual people."
Julia Roberts had great chemistry with Richard Gere in "Pretty Woman" but somehow "Runaway Bride" was not that much successful.