Here is a great theory about why Rumple needed the true love potion: https://oncepodcast.com/forums/viewtopic.php?f=19&t=359&p=2465#p2465
Also, I think perhaps Rumple knows the future on a limited basis, as King Arthur suggested. Perhaps his foresight is dependent upon the subjective free choices of others (as he’s fond of saying “everyone has a choice.”)
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy