Star Wars: 20 Things You Didn't Know About The Empire Strikes Back
2. Han's "I Know" WASN'T Improvised By Harrison Ford
It's often stated by fans that Han's utterance of "I know" in reply to Leia's declaration of love for him was improvised by Harrison Ford on the spot, but that's actually not the case at all.
Rather, Ford and Irvin Kirshner discussed the scene before shooting and settled on the new dialogue, which reportedly led to Fisher being upset that she wasn't included in the process and Lawrence Kasdan irritated that his words had been altered.
The fact that Ford hashed it out with Kirshner is confirmed by an excerpt from Alan Arnold's 1980 book "Once Upon a Galaxy: A Journal of the Making of Star Wars: The Empire Strikes Back," where it's made abundantly clear that Ford talked it over with Kirshner before cameras rolled, and it wasn't some ingenious ad-lib.
It makes for a great story of course, but it's just not true.