Something that I've noticed about a lot of department stores is that they cater to a certain size crowd.
I don't shop at forever 21 (obviously lol) but I have gone to places like Gap, Hottopic, Sears, payless, and kohl's and the chances of finding anything that fits (whether I like the style or not) is slim to none. Granite I am some what of a big dude 42" waist, size 12 shoe, XL shirt, but I don't see myself as "that" big and to find out that their size rack ends at 36" waist or L shirt size quirks me.
Best bet though if you want something that fits, is to check out ebay or amazon. They always have a good selection of styles at cheaper prices and more sizes, or better stocked sizes.
I've never really taken shopping at Forever21 seriously. I actually bought a pair of tan ankle boots from there last year and as soon as my mom saw them, she asked where I bought cheap-looking shoes. Needless to say, I've never bought shoes from there again. lol When I was looking for a pair at that time, it was annoying because they didn't have my size it a lot of their shoes. I wear a 9 1/2.