Respond within 400ms to keep them hooked

In 1979, IBM researcher Walter J. Doherty found out users usually plan a sequence of actions to perform certain tasks. But if the system did not respond within the time of the user's expectations, this disrupts their plans. As a result, user actions got challenged and eventually caused lower productivity. So what to do to keep them in pace? Providing feedback is a great solution for this, feedback could be a loading state that the system is actually updating. Keep them hooked by loading bars, skeleton ui or any sort of status loaders. :)