When a user has the ability to do something but does not want to, the right prompt does not tell them what to do -- it reminds them why they care. That emotional nudge is a Spark, and it is one of the most powerful tools in persuasive design.
Think about the last time you didn't go to the gym even though you had the time, the kit, and a perfectly clear schedule. The ability was there. The motivation wasn't. Someone telling you “go to the gym” in that moment wouldn't have helped. But seeing a photo of yourself from five years ago, feeling the pull of a goal you'd set, or a friend's message saying “I just did my best run ever” — any of those might have actually moved you.
That's a Spark. In BJ Fogg's Behaviour Model, a Spark is a specific type of prompt designed for situations where someone has the ability to act but lacks the motivation. It doesn't tell you what to do. It reignites why you wanted to do it in the first place. It appeals to emotion, identity, aspiration, or fear — whichever motivational lever is most likely to get the person off the fence.
Fogg's model says behaviour happens when three things come together at the same moment: Motivation, Ability, and a Prompt. When all three are present, the behaviour happens. When any one is missing, it doesn't. The type of prompt you need depends on which of the other two is missing. If motivation is high but ability is low, you need a Facilitator — something that makes the action easier. If both are high, a simple Signal is enough. But if ability is high and motivation is the bottleneck, only a Spark will do.
“A prompt sent without motivation is just noise. A Spark arrives when the person needs to be reminded why they care — not told what to do.”
— BJ Fogg, Tiny Habits, 2019
A fitness app user hasn't logged a workout in 9 days. They had a goal to work out three times a week. Their streak ended. They have a gym near them, free time tonight, and their kit is packed. Ability: high. Motivation: low.
Below are three push notifications the app could send. One is a Signal (just a reminder), one is a Facilitator (makes it easier), and one is a Spark (reignites motivation). Only one is calibrated to the actual problem.
The Spark works not because it is cleverly written, but because it diagnoses the actual problem. The user isn't stuck because they don't know what to do or because the app is hard to use. They are stuck because the motivation that got them started has faded. The Spark reaches back to that original motivation and pulls it forward into the present moment.
Sparks aren't only for habit-building apps. Any situation where a user has the ability to act but lacks motivation in the moment is a Spark opportunity. Donation platforms face this constantly — a user visits, sees the cause, understands the need, knows how to donate, but doesn't. The ability is there. The motivation lapsed somewhere between “I should” and “I will.”
Below are two donation prompts for the same campaign. The first is informational — facts and a button. The second is a Spark — it connects the user to a specific person, a specific outcome, and a moment that only exists right now. Same cause. Different emotional pull.
The Spark version works through four mechanisms: specificity (Amara, not “millions of children”), proximity (the deadline is real and close), near-completion pull (89% — they're almost there), and identity framing (“help finish” rather than “donate”). Each of these is a motivational lever. None of them changes the product, the price, or what the user has to do. They only change whether the user feels moved to act.
Before designing a prompt, ask: what is actually stopping the user right now? If the answer is “they don't know about this feature,” a Signal (a simple notification or tooltip) is enough. If the answer is “it is too complicated,” a Facilitator (a shortcut, a default, a simplified path) is what is needed. But if the answer is “they know, they can, they just don't feel like it right now” — that is when you need a Spark.
The best Sparks are specific and personal. They reference what the user actually did, what they actually committed to, or what they are actually close to. Generic motivational copy (“You can do it!”, “Don't give up!”) is almost never a Spark — it has no specificity and no emotional hook. A real Spark says: here is exactly where you are, here is exactly what you wanted, and here is the gap between the two.
Fogg, B. J. (2019). Tiny Habits: The Small Changes That Change Everything. Houghton Mifflin Harcourt. Fogg, B. J. (2009). A behavior model for persuasive design. Proceedings of the 4th International Conference on Persuasive Technology. Small, D. A., Loewenstein, G., & Slovic, P. (2007). Sympathy and callousness: The impact of deliberative thought on donations. Organizational Behavior and Human Decision Processes, 102(2), 143--153.