system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 why do people have Aphantasia?

I recently got told that people are actually able to visualise images in their head, something which I cannot do, which brought me to the condition of Aphantasia. 

Why is this something that I cannot do?
gpt
First off, you have to narrow it down. There's actual aphantasia, and there's people who read a poor  overly-romanticized description of what visualization is and conclude they must have aphantasia. The former is extremely rare, the overwhelming majority describe normal visualization as what they're able to do and assume everyone else has some sort of superpower that they're missing.