When we gift a new acquaintance with the profitable question "What do you do?"
the human brain kicks in.

We are willing to listen to someone else talk about themselves
for about one minute.
At one minute twenty seconds we begin to think about what we're going to say
when they shut up.
At one minute forty seconds we begin actively looking for them to take a breath
so that we can interrupt.
And at two minutes we're finished.  We stop listening. 
Sometimes we even forget what they are talking about.
The worst thing is, if they called us tomorrow to follow through
we wouldn't remember the conversation.

Now you understand the cliche "he talked himself right out of the sale".
More important, you know that happens at two minutes.