The right stitch for the right yarn
I don't think I have ever knit from a pattern and used the recommended yarn. I generally try to use something from my stash, and in this instance, just as when designing a new pattern, you need to swatch. Not to determine your gauge [like I've talked about before here and here], but to make sure the yarn you're using likes your desired stitch pattern. Some yarns have better stitch definition than others and some stitch patterns have more or less give and require a yarn with a certain amount of squish. So, don't be afraid to switch things up, but do take the time to swatch.
[These swatches are from the planning stage of poppy's socks]