Here's my real world example that seemed to break everyone's brain...I had a room in a house that I wanted two ceiling fans installed in, in a line, with even spacing between the fans themselves and between the fans and the walls at each end.
Everyone I called over to do said work said easy peasy, measure wall to wall, divide by 3, done and done.
I tried to explain this centers the bases, but then the fans will be closer to each other than the walls, but they'd either argue or just roll their eyes.
I finally just marked the ceiling myself, and found a person to do the work without asking why or arguing. Ah, perfectly spaced fans at last.
To better understand how people might get confused... Imagine a room 9 feet <insert your favorite unit of measure> long and fans 2 feet in diameter. If you put them with bases equally spaced—3 feet apart—you get a gap 2 feet between the wall and fans… but 1 foot spaced apart in the middle.
Naively, you move each fan a half foot closer to the wall. This makes the gap 1.5 feet to the wall but now 2 feet between each other. (You might find ways to argue that this looks better visually than the true answer below, and that depends on a lot of perception-altering factors including how low the fan hangs from the ceiling, amount/ratio of space available, the distance from the non-perpendicular walls, and light sources as they might cast shadows with different sized gaps on the ceiling.)
You need to take the total room length and subtract the fan diameters, then divide that by 3. (So, 5 / 3 = 1.667 or 1'8" from wall to blade tip.) Thus, each base should be 2.667 feet from its nearest wall. This makes a gap 1'8" between each blade tip:
Bringing this around to the theme of web design, this is akin to space-between, space-around, and space-evenly in justify-content[1] (except there isn't a "space the center of each element evenly" selection, except maybe stretch or nesting everything in another flexbox)
Everyone I called over to do said work said easy peasy, measure wall to wall, divide by 3, done and done.
I tried to explain this centers the bases, but then the fans will be closer to each other than the walls, but they'd either argue or just roll their eyes.
I finally just marked the ceiling myself, and found a person to do the work without asking why or arguing. Ah, perfectly spaced fans at last.