How could internal conflicts in stories be helpful to us in our own lives?

It isn't essential. It is merely one of the options that a writer can use for his plot.

Consider 'The Hound of the Baskerville's' there is no internal conflicts in this story. (Maybe a little in the servants.)

Consider Hamlet Macbeth and Othello. Internal conflicts galore - as that is the conflict that the play write choses to exploit.