For most things you want to knit, someone somewhere has already written a pattern. Meaning that most of the time there is no reason to reinvent the wheel. You just follow the patterns that already exist. But even then, sometimes we can't find exactly what we want, or the yarn we want to use doesn't quite fit the pattern specifications, or the offered sizes might not be quite right. In those cases, we can still use the pattern and the yarn we'd prefer. We just have to take a few minutes to think about how to adjust the pattern to fit exactly what we're trying to do.
Maybe the yarn you have chosen isn't quite the right weight for the pattern. I say always use the right size needles for the yarn, not the pattern and go from there. Make a gauge swatch and calculate your stitches per inch. If your pattern is a simple stockinette or garter stitch, you can just add or subtract the right number of stitches after comparing your gauge to the pattern gauge. If your pattern is a repeat, you'll need to add or subtract consistent with that repeat. So if the repeat is an 8 stitch repeat and your gauge is off by 6 stitches, you'll need to add or subtract 8 stitches. Be careful, then, if you're subtracting because you might be better off with the project being a tad too big rather than a tad too small.
The lesson: You can adjust a pattern to fit your yarn choice, you just have to put in the time to do it right.
I once wasn't sure about which size sweater to make for my dad. Length-wise, I thought he was a medium, but I also knew the number of stitches for the large size would work better. So I used the medium size measurements with the large size stitch counts. I went through the entire pattern before I started, to make sure there wouldn't be any surprise points where this method wouldn't work. It was a long pattern, with lots of pieces, so this part was tedious, but the end result was well worth it.
The lesson: if the sizing on a pattern doesn't seem ideal for your project, you can adjust. The online knitting class, Fit Your Knits, can help you learn how.
Dad's sweater came out great.
Once, I had a specific type of sweater in mind. I wanted to make a hooded pullover sweater for a little boy, but the only pattern I could find was a cardigan hoodie. The hood itself was an add-on, so I knew I could just modify the pattern from a cardigan to a pullover. At the neck opening on the cardigan, the pattern called for some bind-offs where the neckline would taper a bit. Sadly, I didn't think that one through, so my finished sweater, while still cute, has an odd little pucker at the front. For a pullover worked in the round, no bind-offs should have happened. Craftsy's online knitting class Knit to Flatter can help you make every sweater your new favorite.
The lesson: it pays to read the entire pattern first and think about every shaping element if you're adjusting the garment structure in some way. I know I won't make that particular mistake again.
The bottom line is that any pattern can be adjusted. But if you're going to make pattern adjustments, you want to think through the implications of those adjustments all the way to the end of the pattern. The more time you put into thinking through your project before you cast-on, the better the result you'll get.
Have you ever modified a pattern, either to great effect or to disastrous results?