Test your judgement
An upload takes three seconds you can't speed up. Which version keeps someone with you?
Someone taps "Upload" and the file genuinely needs about three seconds to send - you can't make it faster. Pick the version that keeps them waiting calmly instead of wondering whether it broke.
Version B works better here. The upload takes the same three seconds either way - but the blank screen leaves you guessing whether your tap even registered, so you wait, doubt, and often tap again. The moving bar answers inside the moment: yes, it heard you; yes, it's working.
That's the Doherty threshold: keep a system responding within about 400 milliseconds and people stay in flow; cross it in silence and attention breaks. When the work itself can't beat the threshold, you make the response beat it - feedback that something is happening buys back the wait.
The honest caveat: the feedback has to be truthful. A bar that stalls at 99%, or fakes progress it isn't making, costs more trust than it earns. And for waits already under the threshold, a spinner that flashes for a tenth of a second is worse than none at all - let fast things just be fast.
See all the checks · warm up in the glossary or test the terms on the quiz.