Aperture scales are handy to use as a quick reference, but they’re not the final say in how you should pick your f-stop. The truth is, there’s no single f-stop you should shoot with for any given scene. It’s a balance between your shutter speed, ISO, and aperture, and it comes down to how you want the photo to look.
If you’re shooting an indoor event with low light, you might want to stop down your aperture. But you also might not want a shallow depth of field. To keep everything in focus, you could shoot with a flash and keep your aperture in a medium range, or crank up your ISO to compensate for the low light. You could also slow down your shutter speed to let in more light.
With all of these settings, you have many options when it comes to setting up a shot. It’s a bit like solving a puzzle with different variables, and learning how to work with light takes a lot of trial and error.