The hardest thing about dressmaking is fabric selection. Fabric selection for a quilt can be tricky, but that's purely a design thing. Even if you've got the most horribly clashing prints imaginable, as long as you're using 100% cotton with a shrinkage rate of less than 5%, you'll end up with a functioning, if not necessarily aesthetically pleasing, quilt. When it comes to making clothes though, fabric selection is waaay more tricky.
It's all about drape, see. I hate drape. Partly cause I don't really have the figure for it (ie. I'm a boobless stick) and partly because it's pretty much impossible to economically design an item of clothing with drape without a mannequin. Ever tried to pin clothes around yourself? It doesn't really work. And making the same item over and over again doesn't work either, because fabrics with drape are usually about the same price as quilt shop cottons, and the cheap stuff you use for making your practice muslins doesn't drape.
I remember now why I didn't go off and do fashion design. That next batch of monsters might get made sooner than planned. At least they always work.