What you need to know
Slow networks make people click submit more than once. Duplicate requests can create repeated orders, messages, or records unless the UI and server both account for retries.
How to apply it
Disable the submit button while the request is pending, show progress, preserve field values after a recoverable error, and add an idempotency key for operations that must not be repeated.
Common mistake to avoid
Client-side disabling is not a security or consistency guarantee. The server should handle duplicate requests safely for important actions.