This is the #1 heuristic in the old Nielsen usability principles. It's called 'visibility of system status'. Users have been trained by years of experience tha

This is the #1 heuristic in the old Nielsen usability principles. It's called 'visibility of system status'. Users have been trained by years of experience that errors are often immediate, while real 'work' takes a little while to happen. From that POV the conclusion is correct - adding an artificial delay is the common solution, though it can also be handled by other forms of feedback. In this case, the success message is appended after the form. A few tweaks that could help: - make the fields become read-only after submission - hide the submit button after success - replace the whole form with the success message These would help both to eliminate confusion, without the introduction of artificial delay, and to prevent double submission.