As a moderator of several groups that do squares from various books, I keep running into “Oh, I want to do these but I don’t have the weight/color/brand/style yarn they mention.” That shouldn’t stop you from making something. A different kind of yarn will make a different feeling square most likely, but that doesn’t make it “wrong” or substandard.
I like to think of a pattern as a suggestion. They tell me the steps used to make an object, but I’m highly unlikely to use the colors they recommend, or the arrangement they show, or even the hook they suggest. Crochet is a creative endeavor. Even if you’re following a pattern someone else wrote, you can make it uniquely yours with yarn choice, hook choice and color layout choice. This is very apparent in our Block a Month Cals. The same pattern turns out squares that don’t look remotely similar to each other because of the different styles of the stitchers and the colors that appeal to them. Squares that are written with suggestions of bright colors, become absolutely stunning done in a single color and vice versa.
Don’t let patterns paralyze you. It’s hard to choose color sometimes but you know, if you make it and you don’t like it, you can try again! Or you might find that oddball colors you have lying around might turn out to make something spectacular.
To me, crochet shouldn’t be stressful! It should be a fun and rewarding endeavor that lets you be creative while making something that can be useful or just sit on your desk to make you smile. Getting twisted up about having exactly what the book calls for only puts a roadblock in front of something that might turn out to be wonderful with the things you have on hand.