A deck is a list of claims. A demo is proof that at least some of them are true. The gap between the two is enormous, and everyone in the room feels it.
Founders over-invest in slides because slides are safe and finished. A demo can break in front of you, which is precisely why it is convincing when it does not.
Show the thing working, even roughly, and the conversation changes.
When You Have No Demo Yet
A narrow slice that genuinely works beats a broad vision that only exists on slides.
Build the smallest real thing you can point at.