Optimism
The optimal state of mind is optimism. [1][2][3][4]
This doesn't mean unrealistic optimism, which leads to bad decision making. It is the hopeful optimism that things will continue to improve and self-correct, and people's lives will get happier, society will become more just. It is looking back on the events of your life and seeing them in the best light, where negative experiences turn into opportunities to learn, grow, or build resilience. It is the belief in an omnibenevolent universe that becomes a constant source of wonder and awe.
When you are happier, you have more motivation and energy, and you can do more to actually achieve the goals and bring about the changes you are so hopeful about. This is the type of optimism that becomes self-fulfilling.
Learning Optimism from a Book
The book by Jamil Zaki, Hope for Cynics is an excellent primer on hope, optimism, cynicism, and the effects these dispositions have on our brains. This interview on Plain English gives a good overview of the topics discussed in the book.
Stephen Pinker's The Better Angles of Our Nature is another book that makes a strong case for long-term optimism about humanity.
Automatic Optimism
The God Concept explores the how belief in omnibenevolence and the ritualized reinforcement of the goodness of the universe helps foster a lifelong sense of optimism.
Taking psychedelics has been shown to increase optimism in rats.[5] Might work for humans too.
Optimistic Videos
A lot of content related to optimism comes from the sales training, motivational speaking, and self-help world. This makes sense because optimism is a key factor in career success. However, this does mean that a lot of it is people trying to monetize ideas that you can easily learn for free, with a fair amount of pseudoscience and woo mixed in. While this content can be very uplifting, avoid getting grifted and move on once you hit their paywall.