To pay it forward, you give for the sole benefit not of yourself, but of your children's children's children. This has been associated with (in part thinks to the semi-campy film of the name) wild karmic Random Acts of Kindness, but doesn't necessarily by the original definition.
The weird thing about our culture is that somewhere in the last half century we suddenly (in economic timescales) started paying it backward (in a cultural sense, at nearly every level). The modern credit system has enabled us to spend now, for the sole benefit of ourselves, and leave the burden of payment to ourselves at a later date. It's amazing really, how short-sighted it is. On the other hand, it isn't hard to see why the often Armaggeddon-obsessed Conservative backward-lookers often don't see a problem with this sort of "ownership society" in which what I have now is based only on the potential of what I might have in 50 years.
Debt has become a reverse commodity. The sure irony of it all is that even with its IOU nature, which to the average person says that it is worth less than the money it takes the place of, debt has become in some cases more valuable than the money it represents. Visa freely gives you that $15,000 credit this year because it is really worth more than that to them. What's more, after brief "trustworthiness verification" they manufacture as much debt as free and easy as they want. In essence, Visa is printing an equivalent of money for free whenever they feel like it and their "feel like it" revolves solely on the potential of a person and their assumed trustworthiness to pay it back(ward). In economic theory, in the end (the far long term) this all balances out and every dollar created is paid back and the "created" money vanishes away again, as it was only a virtual shadow to begin with. In economic reality, these sums of created money in the short term don't really vanish and the virtual nature of the money make it just as "real" as the dollar itself, which in the modern world has no inherent value other than the value it has in the market with respect to the other currencies.
Let me pause here to let you ponder the last paragraph. I realize it is a doozy. I'll leave you with one last example to ponder, if you still don't believe the last paragraph: some companies are making quite a bit of "real" money buying and trading the debt of others. How is it, if debt is not a commodity, that there is a market for debt under the name of "debt consolidation"? Interesting to note, even though having short term losses of "real" money, the Asian markets continue to buy American debt.
The question becomes, how do we use this to our advantage rather than long term detriment? This actually has been discussed since shortly after the Great Depression and has been referred to as the platform of Social Credit. Social Credit had a few successes in Canadian politics, but hasn't been heard of much in America in several decades. Social Credit asks us to wonder: what if this power to create virtual money (like loans and credit cards) was taken away from the Corporations and given to solely to a non-profit group or perhaps a smarter reverse-IRS? Suppose that credit wasn't given solely based on a person's potential income (based on things like education at the moment and job at the moment) and instead of a person's need. For example, everyone, outright, gets, say, $400 a month (the basic needs of a normal person for food, shelter, emergency healthcare) "credit" (assume the group in charge just doesn't care to be repaid, it is "paying it forward"; which would require the power of the mint, really), but those who demonstrate a need and a wish to improve their lives (poor living in a rundown house looking to improve it) get more. Others have explained it better than I can, but that should give you an idea of the basic theory. The theory isn't socialism, it's a relative (and some might say a stepping stone), but it still depends on capitalism for distribution and allocation of resources (socialism has a hard time dealing with the scarcity of certain resources, as long as there are major issues with scarcity there will never be true socialism; the only proven working model is a mixed capatilistic/socialistic economy to deal with wants/needs (respectively), and this was proven without a doubt in this country by FDR). The only capitalism harmed by such a system is that the current Banking/Credit Card industries would have to be severely crippled.
So there's my Mixed Economy spiel and why we should be using the commodity of debt to its best advantage. Feel free to tell me why you think I'm a moron and it will never work. But first, take a few minutes and research Social Credit. If you want a cool usage in a good (but not great) fictional account, read Robert Heinlein's last/first novel For Us, The Living.