Rather interesting to read this (US) Craft Yarn Council research on knitters/crocheters, why and what they're making. Stress relief features as a significant reason. But the top reason? A feeling of accomplishment.
Follow the link to read more. (I did have a little wee chuckle that more crocheters than knitters completed the survey - doesn't mean there are more of one than the other, but it's always rather fun to see crocheters in the majority!).