I have no problem with the Pay it Forward concept. I love giving to church, charities, etc. I have a problem with the guilting and shaming that some of these have become. I can't stand Starbucks coffee, but one day I wanted something hot to drink so I drove through and ordered a hot chocolate. When I got to the window, they said the person in front had paid for mine and they had been doing the Pay it Forward all morning. I asked how much the person behind me owed. She said $15 something. I said, I don't think so. She then said, but you have to.....it's been going all morning. I said (politely), no I don't. I have $2 to pay for mine, but I don't have $15. She said, but you'll mess it up. I said, all good things come to an end, I guess. She wouldn't even take my $2.
If it's spontaneous (and I've done things like that in the past), fine. It's a great blessing to somebody out of the blue. I usually only do it when I'm inside and know specifically who I'm helping. I did it one time for a mom chasing around 3-4 kids one day in Chick-Fil-A. I could tell it had been one of those days and she was struggling. After I paid, i slid the kid a $20 bill, and said apply that to the lady's order behind me. I don't say that to pat myself on the back, but to spotlight the real point of Pay it Forward's. When it's expected and/or demanded even, it loses it's effect in my opinion.