“Winging” a presentation, making it up on the spot, is extremely hard, and I would say, impossible. All people that seem to get up on stage and deliver a perfect pitch without any effort have in fact been rehearsing this over and over and over. (The previous instances where they pulled off the same trick). You need to practice really hard to be spontaneous.
When you look at a piece of paper with the scribbles of your thoughts, it seems like you have it all in your head. Everything is there. But standing in front of an audience is different. Your eyes are moving quickly across the piece of paper, going back and forth if relationships are not clear. With speaking, there is no rewind option. You need to build that “visual” in people’s minds step by step.
Many things can go wrong here:
You forgot the exact sequence of your points and you realize it too late, now you are stuck without a way to go back
You get distracted and are not sure where to pick things up, as you try to get your thoughts together, you repeat a few things you already said
You delivered that powerful punch line too early and now your speech ends with a mumbling “well, that’s it, thank you”
Don’t wing your pitch.