I've never had to follow-through with this tip, because from my experience, it works.

Go out planning to turn back after a mile (or a half-mile) if it's too cold/hot/muggy/rainy/snowy/icy/dark/tiring/whatever.

No matter how much I really didn't want to leave the house (let alone ride), after a quarter mile or so, I'm happy to be out and kicking myself for wasting so much energy on dithering.