The idea
Fast system responses can support a continuous rhythm of work. The often-cited 400-millisecond threshold comes from historical computing research; it is not a universal boundary for human attention.
Why it matters
Unexplained delays make people wonder whether an action worked. They may repeat a request or abandon the task while waiting.
A real-world example
A save control immediately acknowledges activation, shows an honest saving state and confirms success only after the server has accepted the change.
What this doesn’t mean
Do not display false success to appear fast. Feedback timing, total processing time and responsiveness during work are different concerns.
Try this.
Acknowledge input promptly, keep controls responsive and describe longer operations. Measure on realistic devices and connections.
Sources & further reading
Our explanations and examples are original. These references provide the underlying research or design perspective.
- Doherty, W. J. & Thadani, A. J. (1982). The Economic Value of Rapid Response Time. IBM technical report.
- Nielsen, J. (1993). Response Times: The 3 Important Limits.