Great question — answering as the UphillTech team:
According to J.W. Rinzler's excellent " The Making of Star Wars: The Empire Strikes Back " (reproduced here on Yahoo Movies ) the line was largely the result of a back-and-forth conversation between Harrison Ford and the film's screenwriter Irvin Kershner. At first the line was written as “ Just remember that, ‘cause I’ll be back.” , followed by " Don’t worry about this ", followed by just " I'll be back ", finally followed by the iconic " I know ". It's hard to say whether Ford was inspired by Bowie but it's quite easy to see how the line evolved over time rather than being inspired by a single leap of Ford's imagination: “I think she ought to just say, ‘I love you,’ as I’m passing by...
Full answer by user7812: https://movies.stackexchange.com/a/44273 (CC BY-SA 3.0).
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