Motivational advice risks making things worse, by surreptitiously strengthening your belief that you need to feel motivated before you can act. By encouraging an attachment to a particular emotional state, it actually inserts an additional hurdle between you and your goal.

Oliver Burkeman in The Antidote, the first 1/3 of which I can confirm is good. After the intro, he talks about Stoicism and the dangers of optimism; this came from a chapter on Buddhism, non-attachment, and mindfulness meditation.