There are two mindsets – growth and fixed mindset. Growth Mindset is the one you want to have. It's enabling you to learn, and to achieve mastery over time. The fixed mindset on the other hand, prevents you from challenging yourself. It means you are accepting things and your current state as it is, instead of pushing and risking failure.
Fixed Mindset – "I can't do mathematics. I never could." Growth Mindset – "Hmm, I might suck at mathematics right now, but it's hard, so I guess that means I need to learn more". Mathematics is just an example, the distinction applies pretty much for anything that can be learned.
The two mindsets are a lense through which we can view the world. The Growth Mindset is about putting in a lot of work to become better. Work is more or at least equantly important to innate ability or talent. The Fixed Mindset is about looking good to outsiders, but not wanting to deal with the real pain of failure, that growth requires. Eventually people in the fixed mindset stop challenging themselves, because they failed a few times and couldn't push past those failures to grow again.
I like how the same idea is phrased elegantly in The Art of Learning by Josh Waitzkin. Humans are like hermit crabs – we live in our shells, not wanting to go out of them. But to grow, we have to abandon our shells, which is painful and makes us vulnerable. The difference between growth and fixed mindset then is, how much we cling to our shells and resist growth because we fear the pain associated with it.
Growth mindset people are more successful in the long term. Most people don't have a growth mindset. However growth mindsets can be learned over time. Simply being aware of the distinction already helps. Catching yourself, having self-limiting beliefs of the fixed mindset sort also helps. Pushing yourself to grow, and not accept who you are right now as a fixed thing also helps. Simply working on something, trying to become better at it over time, and thinking hard about how to deliberately push yourself into situations where you might fail and learn from that failure also helps.
A lot of the Growth Mindset ideas come from school and childhood. In school we get rewarded for doing less. The less you do, while still getting good or good enough grades, the more of a "genius" you are. We adore geniuses and don't focus on the hard work, but instead on the "genius" part. We tend to focus more highly on talent than on work. This is a fixed mindset belief. This idea, and why it is wrong is dismantled more in Malcolm Gladwell's book Outliers. There he also adds that while hard work is important, luck also is. Sometimes equally or even more so. Something that the Growth Mindset doesn't focus on too much. But still work > talent. Talent is only a multiplier – if work is 0, it doesn't help you.
Another lens to look at Growth and Fixed Mindsets is from a game theoretic point of view. Fixed mindset people like playing zero sum games. The fixed mindset is about beating others. It's about looking good on the outside. It's mostly focused on winning.
Growth mindset people are more interested in the game itself. And how good they are compared to yesterday. Not for the sake of winning it, but for the sake of becoming better at the game themselves. Because they love the game. Incidentally this often leads to those people performing better in the long run. People who win at something like the Olympics are very rarely fixed mindset people. Instead they are people who have the talent, a growth mindset, put in the work, constantly grow and improve and have had some amount of luck in the past.
The self-worth of growth mindset people is not fundamentally tied up with the games they are playing. They can lose, and take lessons from the losses. They focus not on the loss itself, but how it can be framed as a learning. Because of that "losing face" stings much less to them. For fixed mindset people, those situations are absolute disasters, sometimes scarring them for life.
Growth mindset people can enjoy infinite games, fixed mindset people have a harder time doing so, because if the game is about continued play, they are forced to view their own shortcomings eventually. And that just hurts too much. So they either start to grow and adopt a growth mindset or they stop playing the game eventually. The same is even true within finite games. If fixed mindset people reach a point after which they can't compete anymore without serious efforts for improving, and start failing more regularly, they just stop playing the game, or keep playing it at this lower level, "never really trying" and inventing excuses for themselves and others. Basically thinking, if only I were trying, I would succeed, but I don't really want to try so badly. Because there are other things more important to me. They save face by shifting their goal posts to things that are definitely reachable, where repeated failure is not in the set of possible options.
All of these ideas are painful to me, because all to often, I see myself thinking in fixed mindset patterns. A big part of my life has been defined by fixed mindset thinking and only slowly but surely have I been getting better at thinking differently. So far, this ongoing change has been nothing short of enabling for me. But I am still far from where I would like to be.
Still... The book, overall, was only decent. Hence the rating of 5. I don't have detailed notes on it, but I remember that the central idea, as I described in the summary was about all there is to this book. It's a branch book, good for one idea, that can also be gleaned from a summary, and that idea can lead to a very powerful shift in mental models. But it's limited to that one idea only.