Goal-Gradient Effect
We put in more effort when we see that we're getting closer to our goal.
The research
In a field experiment, researchers distributed 300 loyalty cards to car wash patrons. Half of the cards required 10 stamps for a free wash but came with 2 free stamps. The other half required 8 stamps. While both required 8 stamps for a free car wash, patrons that received the loyalty card with 2 free stamps returned faster for their next stamps and were 15% more likely to complete the card to receive a free car wash.
Nunes et al. (2006). Your loyalty program is betraying you
While rats run faster as they approach food, humans raise their game when approaching a goal.
Thought starters
Show people that there is a visible finish line and give them bonus points for starting
Tailor the experience for the individual
Show people what they will miss out on if they drop off
Try combining with (C5) Psychology of Chunking.