My main sprite has never gotten sad with me. It's only been "normal" mood with me about four times total.
What I do is just send it out on jobs until it gets to about 10-15% stamina left, then leave it alone til about 50%, then send it out more.
Sometimes I feed it the biscuits when I'm training so it can keep picking up my drops.
If the sprite fails while doing a job, I leave it alone for maybe around 10 mins.
My sprite's been ecstatic MANY times, and gets a LOT of positive events if I continuously do the same job over and over with it.