Picking up The Bright Side, I didn’t expect much in terms of depth or sophistication. Optimists see the glass as half full, pessimists as half empty, and countless wordplays have spun off that euphemism. I was ready for a light, breezy summer read—but it turns out my expectations were mostly misplaced. Sumit Paul-Choudhury offers a rich and thought-provoking exploration of a surprisingly complex topic.

What kinds of optimism are there, anyway? Surely there’s a difference between “hoping things will work out” and “working toward a better future.” That distinction—between passive hope and active striving—goes back to thinkers like Leibniz and Voltaire (the latter famously mocking the former’s optimistic theodicy). And it still echoes today in debates about climate change, capitalism, and human progress. Paul-Choudhury manages to cover all that in just 270 pages, weaving in references to ancient Greece, Marx’s theory of inevitable progress, and Paul Ehrlich’s misguided fears about population growth.

But he doesn’t stop at big-picture philosophy. Paul-Choudhury also brings in the role of individual responsibility. Research shows that optimistic people are, on average, more successful than pessimists. But what drives that success is more complex than it seems. Optimists often believe their goals are achievable—and unlike fatalistic pessimists, they take action. That action tends to generate unexpected, sometimes unrelated opportunities. These may not lead to the exact future they had envisioned, but they still produce positive outcomes. In contrast, pessimists often don’t act at all, missing out entirely.

This dynamic offers a fascinating way to examine success. How many startups hit product–market fit only after several pivots? How many great ideas emerged by accident, stumbled upon by founders who simply acted? Yet, there’s a flip side: over-optimism has its dangers. In business and politics, it can lead to the planning fallacy—underestimating time, risk, and potential pitfalls that a pessimist would carefully consider.

So, optimism remains a double-edged sword. Too much, and you end up like Elizabeth Holmes of Theranos—full of hype, but without a working product. Too little, and you’re like the mouse too scared to leave its nest, who starves to death. Would the mouse have been eaten by a cat had it ventured out? Maybe. But just as likely, it might have found food, a mate, or simply enjoyed a sunny afternoon.

My key takeaway from Paul-Choudhury’s thorough and engaging book is this: we need to be mindful of our own disposition. If you’re only seeing the bright side of a new project, take a moment to reality-check with a more grounded colleague. And if all you can see is doom and gloom, maybe it’s time to talk to someone more optimistic—someone who can help you break out of fear and inaction. Who knows what opportunities might follow?