Some demos I nail, I speak right to the thing keeping the buyer up at night and they light up. Other times I fall back on my standard walkthrough and I can see their eyes glaze. I know the good ones are the ones I make about them, but I don't do it every time.
More people experience this than they realize.
Some of your demos speak to the buyer's real problem and some just don't.
If this sounds familiar, the Library can help you find the bigger picture.