If you fail to throw me and make me fall in a graceful aikido way, you just confirmed my statement.
If you throw me around, I would say, that's no aiki, that's just brute force! Hah take that.
So how would you convince me ?
I don't know that I would. "Convincing" is like making the proverbial horse drink water; only it can choose to drink. There's a fine line between trying to convince someone and simply making your case...which to my mind also seems to reflect something about the nature of Aikido, as I've come to think of it. The proof is in the pudding. If I'm able to throw someone around and they say it's just brute force, I guess I'd ask them to throw me around without any brute force. At the end of it all we might not agree about what is what, but at least we'd able to enjoy comparing our respective recipes for pudding.
I would say that tori being able to make aite fall in a graceful way depends largely on aite being able to engage his or her body, but also it depends on a relatively high level of skill on the part of tori, particularly as the intensity increases. "Graceful" is a relative term. If I manage to plant an attacker on his butt, compared to his head, that seems comparatively graceful to me.
I was skeptical of some Aikido movements (note I didn't say "Aikido" itself, which is a much bigger animal and much harder to pin down), and it was only through sustained practice that I learned (something) about the usefulness of those movements.