What is persistence?

The following story is from Clientopia. I do not know if it is real or not, but after reading it you will surely understand what does it means to completely concentrate on your goal leaving behind any doubts...
---------------------------------------------------------------


I have had my company mobile for nearly 2 years, out of the 50 odd calls I've had, only 3 were legitimate, the rest were wrong numbers. This is a transcript of the one man who has called me more than 35 times.

Me: Hello, XXX IT, XXXX speaking, how can I help?

Random: Is that Brian?

Me: No, this is XXXX

Random: Are you sure?

Me: I should think I am. I've never been called Brian, and there isn't a Brian involved with this mobile

Random: Oh, can you put me through to him?

Me: No, as there isn't a Brian here, or in XXX IT

Random: Now I know you're lying, this is the number he gave me, now put him on the phone!

Me: I'm sorry, you've got the wrong number

Random: NO I HAVE NOT! BRIAN GAVE ME THIS NUMBER

Me: Then Brian got the wrong number

Random: I THINK HE KNOWS HIS OWN MOBILE NUMBER

Me: On the current evidence, I would say he doesn't, I cannot help, goodbye. *click*

----

He rings back, I don't answer.

----

12 (!) calls later he gives up. Then calls back the next day:

Me: I'm sorry you've got the wrong number, you rang yesterday several times.

Random: THIS NUMBER WAS GIVEN TO ME SO PUT ME THROUGH

Me: *click*

He has since called back several more times.