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I love this so much! What a great concept! I immediately understood the reference to tying a knot around your finger to remember something, and how post-it notes relate to it.
The only thing I would even think about suggesting is to make the note a little more yellow. It blends into the background a little too much. Since the poster is so minimalistic, the post-it could be slightly brighter.

i agree with more yellow, as the post-it note shown is not the same colour as i associate with post-it note yellow.