What is the 3 second rule in web design?

The 3 second rule says visitors decide whether to stay on a site or leave within about the first 3 seconds of landing. If your headline, layout, or load time doesn't communicate what you do that fast, most people bounce before reading anything.

In practice, that means your homepage needs a clear headline, fast load time, and an obvious next step, all visible without scrolling. Everything else on the page matters less than what a visitor sees in that first glance.