Good point - it's normally people who are either jealous of your good looks, charm, charisma and skill (oh, and your ability to do magic, of course!) who seem to heckle.
The main problem is that it ruins the show for other people.
For sure, we're none of us stupid enough to really believe that a playing card can travel through mid-air and land in your pocket, or even that solid metal rings can penetrate each other. But it's the enjoyment of watching the performance that counts, and most people are there to be entertained.
We know that dinosaurs don't exist (well, except for my ex'es mother...

), but nobody stood up in the cinema during Jurassic Park and shouted 'it's not real - I can see the strings'.
Some people get a thrill out of debunking and humiliating. I'm waiting with baited breath for Magicdiscoman's posts on this thread - because if they're a patch on what he was saying last night, he'll show you how the tables can be turned quite easily.
And as for heckler's getting one over on us magi - the last laugh is usually on them - because they go home wishing they could be more like us
