So I admit, most of the knitters I know don't really have problem finding the next project. It is more of a "Which of the next possible five projects should I work on next?" kind of question. When inspiration hits, sometimes it is in a tidal wave.
This is the only way I know to explain the concept of the "stash" to the uninitiated. Sometimes, you find a yarn in the right color, the right amount, the right fiber blend and (!!!) at the perfect price. You can see yourself creating a sweater/scarf/shawl/socks/tea cozy that will be so (a) beautiful that you will be the envy of all your girlfriends, (b) perfect as a gift for that hard to buy for person, and/or (c) cool in technique/color combination that your knitting group will clamor for pattern and the location of the yarn shop. At this time, it doesn't matter that you have a complicated cable pattern sweater on the needles and that it is likely to take the better part of the year (or lifetime) to complete it. It also doesn't matter that you already have a bag/closet/room full of yarns for projects yet begun. You have hit the trifecta and have this new yarn you will.
Stash expansion is something more than sheer avarice and acquisition. Over the past few weeks, I have been going through the closets in the house. This includes the one housing my stash. As I look at the yarns there, I see the possibilities of what these random little balls will become. I get excited about working on what is to come. Some of them will not be how I first envisioned them. That's okay, because dreams change. I also get a "second wind" for those things that are lagging on the needles. It helps me to see them with new eyes. My stash is a source of inspiration.