Thanks for this. Asking people "how much would you have pledged?" is of course only a semi-reliable method of ascertaining how much someone actually would have pledged. Some people - like yourself - might neglect that fact that they would have been convinced by the same arguments from other sources; others might be overoptimistic about how their future self would live up to their youthful ideals. We try to be as conservative as reasonable with our assumptions in this area: we take the data and then err on the side of caution. We assumed that 54% of the pledged donations would have happened anyway, that 25% of donations would have gone to comparably good charities, and that we have a dropout rate amortized over time equivalent to 50% of people dropping out immediately. It's possible that these assumptions still aren't conservative enough.