A default option — whatever happens if a person does nothing — carries enormous, often decisive weight in real-world decisions, because most people simply don't override the default even when changing it would take only a moment. This isn't laziness in any judgmental sense; it reflects a genuine, predictable feature of how decisions actually get made when a choice feels ambiguous, low-stakes in the moment, or easy to defer.
The practical implication cuts both ways: whoever sets the default in a form, a policy, or a subscription service is exercising real influence over the outcome, whether or not that influence is intended — which is exactly why 'neutral' administrative choices like a checkbox's default state are never actually neutral in their effect.
European countries with organ-donation forms that require citizens to actively check a box to opt out of donation — defaulting to 'yes, I am a donor' — have donation rates near 100%. Neighboring, culturally similar countries that instead require citizens to actively check a box to opt in — defaulting to 'no' — have donation rates as low as 4%, despite broadly similar populations and no reason to think actual underlying attitudes toward donation differ nearly that much between them.