I picked up Influence: The Psychology of Persuasion and Hacking Growth around the same time, which turned out to be less of a coincidence than I thought. One is about how people make decisions. The other is about how companies figure out which decisions their customers are making — and why. Read together, they reinforce each other in ways neither author probably intended.
My notes below won’t do either book justice. The stories are what make both of them stick, and I’ve left most of those out. But if you’re someone who builds products, leads teams, or tries to change minds for a living, these are worth the time.
Influence: The Psychology of Persuasion
Cialdini identifies six patterns that drive human compliance: reciprocation, commitment and consistency, social proof, liking, authority, and scarcity. None of these will surprise you in the abstract. What will surprise you is how reliably they work even when you know they’re happening.
Reciprocation is the one I’ve seen most often play out in professional settings. We’re wired to repay what we receive, and that instinct is strong enough that people will accept a bad deal just to avoid looking like a freeloader. The “larger-than-smaller-request” technique exploits this directly: make a big ask first, then follow with a smaller one. The second request looks reasonable by comparison, even if it wouldn’t have on its own.
Commitment and consistency hit close to home for anyone who’s ever watched a bad project continue long past the point of reason. Once someone has taken a public stand, they’ll go out of their way to stay consistent with it. Leonardo da Vinci said it better than Cialdini: “It is easier to resist at the beginning than at the end.” I’ve seen this kill product decisions and hiring calls alike. The sunk cost isn’t just financial — it’s identity.
Social proof is most powerful when the people doing something look like you. That’s why case studies work best when the customer profile matches your prospect, and why peer referrals outperform almost every other acquisition channel.
The liking chapter is the one I’d hand to every engineer who’s skeptical of “soft skills.” Similarity, contact frequency, cooperation on shared goals — these aren’t manipulation tactics, they’re the mechanics of trust. Authority and scarcity round out the six. Both are obvious in theory and easy to miss in practice, especially when someone is deploying them on you.
That’s the other reason to read this book: not just to influence, but to recognize when you’re being influenced.
Hacking Growth
The central argument is that growth is a team sport. The best results come from combining engineering, data analytics, and marketing in the same room — and most companies keep those functions too separate for too long. I’ve watched this play often. The engineers think marketing is hand-wavy. Marketing thinks engineering moves too slowly. Meanwhile, nobody is running the experiments that would settle the argument.
The most important rule in the book is also the most ignored: don’t start growth hacking until you know your product is a must-have, who it’s for, and why. Skipping that step doesn’t accelerate growth — it just makes you faster at running in the wrong direction.
The experimentation framework is practical. Use ICE scores — Impact, Confidence, Ease — to prioritize what to test. Map every step between a new user and the “aha moment.” Calculate conversion rates at each step. Then experiment with different paths and features to see what works to increase the conversion rate. The drop-off point is almost never where you initially think it is.
One thing the book gets right that a lot of growth content gets wrong: correlation is not causation. Metrics will lie to you if you let them. The discipline is in designing experiments that actually isolate variables, not just running A/B tests until something moves.
Linus Pauling’s line shows up in this book, and it’s worth keeping: “The best way to have a good idea is to have lots of ideas.” The ICE framework exists to help you sort through them quickly, not to replace the generative part.
Both books are about decision-making under uncertainty — one from the inside, one from the outside. If you work at the intersection of building and growing things, they belong on the same shelf.
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