Summary: Prioritized design helps users focus on the most promising choices first.
If everything is equally prominent, then nothing is prominent. It is the job of the designer to advise the user and guide them to the most important or most promising choices (while ensuring their freedom to go anywhere they please).
On today’s Web, the most common mistake is to make everything too prominent: over-use of colors, animation, blinking, and graphics. Every element of the page screams “look at me” (while all the other design elements scream “no, look at me “). When everything is emphasized, nothing is emphasized.