When the situation gets worse then not only the top smartest people but also larger masses begin to take it more seriously to protect themselves, keeping distance, and omitting trips and reducing contacts.
This obviously doesn't apply to careless people or "non-believers" but they wouldn't be much affected by regulations either. So there's always (hopefully) a minority of the population where the virus can spread more easily but once the majority successfully does react it will show positively in the growth curves within about 10 days.
Coincidentally this is also the same time where governments impose strong recommendations or even enforce counter measures. Mandatory shutdowns of cafes and restaurants might seem an effective ordinance but the truth is that by that time most people already refrain from going to crowded places such as cafes and restaurants. And usually there's at least a few points of empirical data from neighbouring countries that those same counter-measures alone won't help limiting the growth if the people themselves aren't in it. It only takes one mask-wearing country to not recover from infection growth in order to make it questionable whether masks help much at all.
Keeping distance seems much more effective than masks. In reality, I've seen that when masks became common place people partially reverted back to flocking together and not respecting a good radius of personal space anymore. Masks probably won't hurt if you need to be close to other people but it would be much, much better to keep the distance in the first place.