You can memorize accessibility rote facts, like WCAG 1.4.3 is about color, and that the color ratio for small text has to be 3:1.
That explains to you the “how” of accessibility
Or you can understand why accessibility rules about color are needed
1) Because color acuity decreases with age
2) Because Color Vision Deficiency (CVD, sometimes also referred to as color blindness) is an issue in most populations.
3) That some people can’t see any color at all.
which will allow you to infer the choices that need to be made.
Understanding the “how” will help you pass certification exams.
Understanding the “why” will help you be a better accessibility professional.
Alt: Uncle Sam meme, man pointing a finger, dressed in a blue shirt and wearing a top hat designed with stars with a written caption: If you know about the accessibility “why” you can figure out the accessibility “how”.