Why do browsers sometimes load pages twice?

You know that thing when you open a new web page, and it'll load completely, only for the screen to go white and the loading to seemingly start anew from scratch, and only when it's done can you start navigating the web site? Ie. the website seems to need to load twice before?

I've had this happen a lot recently, and it happens both on my phone and laptop, so I assume it's the way the web site itself is programmed and not a problem with my particular device. So why does this happen?

via International Skeptics Forum https://ift.tt/3gwUH6u