Last fall, over a cup of coffee, a close friend shared with me the news of his recent engagement. Amid the congratulations and excitement, I began to hone in on the perfect wedding gift: a specialty Italian espresso maker I knew the couple would cherish. I vividly imagined them opening their gift, their astonishment turning into pure glee.

Sadly, that moment never happened. Despite my good intentions, I repeatedly put off purchasing the machine until the wedding was only two weeks away. The perfect coffee maker was now backordered indefinitely, and I was forced to settle for a lesser model that could only produce mediocre espresso and, worse, would induce only the mildest joy. I felt like I let my friends down and began to wonder if my spirit of generosity was tarnished. But in fairness, the spirit was there, even if the follow-through was not.

This same situation regularly occurs in charitable giving (except without the ultimate deadline of a wedding date). Donors face episodes of good intentions followed by poor execution—but with much higher stakes. With nearly 30 percent of giving occurring in December, this intention–action gap is especially pronounced in the earlier parts of the year, leaving charities reliant on inconsistent support.

True, it’s easy to argue that Americans are sufficiently generous; in 2016 individual donations reached nearly $282 billion. While this figure is higher than it has ever been, it masks the fact that many people fail to give as much as they had hoped, or as well as they had planned. It’s what we call suppressed altruism.

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Omar Parbhoo is a senior associate at ideas42, a nonprofit behavioral design lab, where he focuses on charitable giving and civic engagement. He received a master’s degree in international economics from the University of California, San Diego.