I was frustrated once when one of my clients, who’d 
insisted on a high growth stock, called in a panic because 
the stock price had dropped more than 15 percent in one 
day.  I had a hard time convincing him to get rid off it 
rather than cut his losses.

Time when my Clients don't respond to me, I find it 
frustating

Yes, once in my career. when i used to work on CR's I 
promissed to fix a bug in our product that is age old(20 
yrs) well known defect. It took more time than what I 
planed why because thats related to three modules in 
product. I spend over time to get it done on time but not 
in time. i felt very very happy with my work. that gave me 
confidence in my work.