I know I'm not the only one suffering from Mismatched Sock Syndrome.
Here's my problem, though... I used the same yarn for both. Argh.
I know what happened, I think... the number of stitches in the foot of left sock (the one on my foot, that is), isn't right. Too many. I should have decreased back down to match the number of stitches in the leg. Just by eyeballing it, it looks like I didn't.
Naturally, because these socks were worked months and months apart, the first one has been sitting in the cupboard, unexamined, and I didn't know they didn't match. I pulled the first one out to measure and match the length of the foot last night, and discovered the mismatch.
I shall unravel the foot of the left and reknit it.