...there have been times when I have performed Just Imagine, and someone after choosing a green diamond and the card is revealed say, "Did I choose that? I thought I chose... ". These people are completely serious as well, and I don't believe it is a screw up in my performing style.
It's hard for us to know for sure if it has anything to do with your presentation skills without actually seeing you perform the trick. Now, no disrespect to you, but most 13 year-old who post here don't seem to think they have any problems with their presentation skills, even though YouTube provides the world's biggest repository of proof of the exact opposite.
1. If you are performing Just Imagine for a single person... an audience of one... there is a problem with your presentation skills (forget, for a moment, that that's how Sankey does it in the demo, since demos are artificial situations).
2. If you are not emphasising the spectator's choices at the time the choices are made, that is a problem with your presentation skills.
3. If you are not emphasising the spectator's choices again before you go for your prediction, that's a problem with your presentation skills.
4. If you are not getting other spectators involved in confirming and remembering the focal spectator's choices (see item 1), that's a problem with your presentation skills.
5. If the spectator believes that they chose a different color than the color you predicted, that's a problem with your presentation skills (the method allows for that possibility; you have to overcome it).
Those are just some things to think about. I don't want to hijack this thread and turn it into a discussion of "Just Imagine." All I will say further about it is that blaming the spectator for your problems is the easy way out.
Anyway... if you want to massage the essay into a larger statement on overcomplicating your magic, go for it. Simple three-phase predictions like Just Imagine are not a very solid foundation for doing so, though.