The way to remember justify is that in flex-row, justify is along the horizontal axis. And, in word processors like msword, you can set the text to "justify" wh

The way to remember justify is that in flex-row, justify is along the horizontal axis. And, in word processors like msword, you can set the text to "justify" which gives you clean edges on each side. I don't know the history of the word `justify` in flexbox but I would imagine it came from here. So since you know how it works in flex-row, then you know it's primary axis in both. For items vs content: You always have items no matter what. But you don't need to do anything to the entire content besides justify/align until you have multiple rows with flex-wrap. There's simply no effect that align-content could possibly have here. So items is for individual children, and content is for entire rows. So tldr: Justify is like the "justify" option in word processors, and align is the opposite one; you always have items, but aligning the content won't change anything until you have 2 rows/cols. Remember these 2 things and you probably won't forget which is which ever again. (That said, I do often forget if flex starts out row or column, but that's relatively unimportant to know, because the way I get around this is by always adding the direction when I say "display:flex".)