Non-knitters may not know the importance of testing your gauge. It is very important. If the pattern suggests you use size X needles with ABC yarn, it doesn't mean you can't use another brand or that size X needles will be correct for how you knit, especially if you've substituted yarn. The key to the gauge is where it tells you how many stitches and rows per inch your knitting must be in order for the knitted item to be true to size. If the pattern tells you that you need 4 stitches per inch and your sample has 5 stitches, that doesn't seem like much difference until you think that 80 stitches at 4 per inch will make your knitting 20" wide. Five stitches per inch at 80 stitches will only be 16" wide. If this were the case in a front and back of a sweater, your total measurement would only be 32" around instead of 40". Oops! Probably not an attractive fit!
My gauge was correct so I spent two nights watching TV and knitting. There was one error in the pattern, but it wasn't critical, just misleading. After every pattern row it gave a stitch count and in one case it was off. Getting past that, I was happily knitting along but thinking this wasn't going to be big enough when done. Further confirmation of this project's unlikely fit came on Wednesday night when the leader of the knitting group said "That's going to be a hat???".
Here is the finished hat, flat. See what I mean about the lacy pattern being lost in this yarn?
Since I don't think washing my head in hot water will shrink it, this hat is going to a charming young friend in my knitting group who has trouble finding hats small enough to fit her properly. She won't have the lovely silver highlights in her hair that I do, but she isn't aged to perfection yet.