Mind & EverydayFact
Two free stamps make you three days faster.
In 2006 Kivetz, Urminsky and Zheng handed loyalty cards to 108 café customers. One group needed 10 stamps, the other 12 – with two already given. Both had to buy 10 coffees. The head-start group finished in 12.7 days instead of 15.6.
Useful: Don't start projects at zero: list what's already done before you look at the list.
Source: doi.org