I've been working on a great cabled sweater for my son. It will be his first sweater that I've made. I got the yarn for it (Knit Picks Shine Sport) for Christmas, and finally cast on a month ago. I had made a bit of progress, through the first cable repeat, and then realized that I was running out of yarn rather quickly. I was certain to not have enough to complete the project. Turns out that I made a poor calculation when substituting yarn. The original pattern calls for Sirdar's Snuggly 4 ply. That is a fingering weight yarn that comes in balls of about 250 yards each. I used the yardage for Sirdar Snuggly DK, which has only 150 or so yards per ball. So, you can see my error resulted in my not having enough yarn. Of course, that dye lot is long gone. Well, replacement yarn is on the way, and hopefully I will have a new sweater for him this fall!
The lesson here? Make sure you substitute wisely, and double check the yardage.