I'm knitting a dress for Ramona with some old Caron yarn that's, seriously, been in my stash since, oh, I dunno, 2004. Granted, 6 years in my yarn stash is NOT the "oldest" yarn, but I've certainly learned a lot about texture, drape, content, ply, etc since then. And, for the record, it's NOT a bad yarn at all - I just prefer different fibers for my own garments these days.
With all that said, back in 2006 I had started making a cardigan/coat for Ramona with Simply Soft. And when I say "started" I mean I knit up the back, fronts and one sleeve...and even sewed them together and started the front button band on one side. These days, I would have just finished that sucker up in a heartbeat. Back then, well, that's another story. I'm not sure I even put it up on Ravelry - that's how long it's sat in the UFO bin.
So when I went to work on the current dress, I pulled a partially used skein of S.S. out of the bin and started knitting. When that ran out, I started a new skein (after all, I apparently needed SEVERAL skeins of Mint Blue - ha ha). But when I got to the armhole split (as I've been working in the round), I didn't want to start another new skein to make the sleeve caps so I said "reuse and recycle" and grabbed the old cardi and started taking it apart (since it would now be way too small for Ramona if I finished it). This gave me a chance to see how I used to seam and finish - and boy...it was B-A-D! Yikes! It was nice to see that I've learned new and "right" ways to finish garments (mostly thanks to Jill at Kaleidoscope Yarns).
I certainly won't regret not finishing that old cardi, but I will remember where I've been and where I'm going...and that's always important on this journey we call life. We DO live and learn (or knit and learn as the case may be).
Have a great day!