John Medina, the author of Brain Rules, says this: "The brain naturally focuses on concepts sequentially one at a time."

How you structure the content on your pages matters. Start with a clear introduction to explain what it's all about (value proposition promise), followed with the body of your presentation (sales copy) and finish with a conclusion, direct your audience to what's next (call to action).

The sequential flow makes it much easier for your audience to follow and keep their attention. When the text is unclear, too complex or disjointed your audience has to work hard to make sense of it. This is when they start to switch off.

All in all people are unable to focus on something for more than 10 minutes at a time. You need to close the sale before that (or do something emotionally relevant at each 10-minute mark to regain attention).