That it is not very convincing

To what he refer when he says that it's not very convicing? I would apperciate if you can help me, this is for my studies, I'm working my way with this video thanks

You can use notes. But then, if you use notes, you often would consult them, and people would see that it is not very convincing, that you need something to aid your memory. And I think that we can do better. And I think, as limited as our memory might be, I am sure that you can still recall the little memory feat in the beginning.

At 4:30