Snyder, "Hope Theory: Rainbows in the Mind" : https://psycnet.apa.org/record/2003-01827-001

Teresa Amabile, Steven Kramer, The Progress Principle: Using Small Wins to Ignite Joy, Engagement, and Creativity at Work : https://www.goodreads.com/book/show/11721498-the-progress-principle

Pim Cuijpers, Annemieke van Straten, Lisanne Warmerdam, "Behavioral activation treatments of depression: a meta-analysis" : https://pubmed.ncbi.nlm.nih.gov/17184887/