🏃♂️ Goal Gradient Effect:
Efforts increase closer to task completion.
Duolingo
Scorestreak
People often become more motivated, the closer they get to their goal (i.e., milestone or achievement).
The key is that they can see their progress—this is why progress bars and step-indicators are so influential in design.
Conversion rates
As you get closer to your goal, you're likely more motivated to reach it.This is partially due to the investment you've already made in the process (the sunk costs).
Habits
Loyalty programs help create habits (e.g., "I always get my coffee from Starbucks"), by motivating the user to return to reach a goal (a free coffee).
Effort & motivation
You may even be willing to exert more effort to reach your goal, as you progress. (e.g., you might walk a bit further to get to Starbucks, if you know that you're only one stamp away from a free coffee).
Feature usage
As you're taking a lesson, Duolingo will show you your score streak.
This isn't your typical 'progress bar', because the score streak is independent to overall progress.
Instead, it's a clever way of reframing "you have 7 questions to answer", by making it pleasurable to reach your goal.
