For comedians, laugher is their feedback mechanism, it's how they tell whether the things they've done has worked or not.
The trouble is that laughter can happen for so many different reasons.
So despite the fact that in some ways comedians are lucky to get immediate, incontrovertible feedback on their work – people laugh or they don't – it's also really difficult for them to understand that feedback and determine exactly what it is made the people laugh.
I guess this is why it takes stand-up comedians so long to develop their skills and to be able to reliably make rooms of people laugh. Like those fire-fighters who can sense a house is going to collapse, they have spent so much time on the job that they that trained themselves to pick up cues that sometimes not even they are able to consciously describe.
I think also this leads to a kind of mystical attitude to laughter and how it's created.