Yarn question

Hi.I was wondering if a person has to worry about the yarn weight .the fiber content being too stiff on a pattern?and the drape?

Sure, that’s always a consideration. Are you substituting yarn in a pattern? If you use a thicker yarn, it will create a stiffer, thicker fabric (and be harder to get into the stitches). If you use a thinner yarn, it will be thinner, with more visible holes throughout, and more drape.