Back in my lab, we'd seen the benefits of giving spike when people felt a real sense of connection with those they were helping and could easily envision the difference they were making in those individuals' lives.
For example, in one experiment, we gave participants an opportunity to donate a bit of money to either UNICEF or Spread the Net. We chose these charities intentionally, because they were partners and shared the same critically important goal of promoting children's health. But I think UNICEF is just such a big, broad charity that it can be a little hard to envision how your own small donation will make a difference. In contrast, Spread the Net offers donors a concrete promise: for every 10 dollars donated, they provide one bed net to protect a child from malaria. We saw that the more money people gave to Spread the Net, the happier they reported feeling afterward. In contrast, this emotional return on investment was completely eliminated when people gave money to UNICEF.
So this suggests that just giving money to a worthwhile charity isn't always enough. You need to be able to envision how, exactly, your dollars are going to make a difference.