I rounded up; I would give this 3.5 stars. It was a decent book with some great principles, but unfortunately it felt much more dated than How to Win Friends. My biggest complaint is that this book had wayyyyy too many anecdotes about how worrying gives you stomach ulcers. The last few pages (or last 40 minutes, in the case of the audiobook) were nothing but stories about sick people getting better after they stopped worrying. I got the message the first 20 times, thanks.

The principles themselves are good ones, though the book is strongly historically situated.

I skimmed many of the stories and even a few of the chapters, as I found much of it to not be very relevant to my present situation. Some parts were also quite repetitive.

This being said, I have to insist that the principles are highly relevant and timeless, and I would recommend this book to anyone looking for some practical techniques on how to decrease the stress that comes with endless worry.

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This book has not aged well and at times was comical. Nothing new learned and constant story after story that are not relatable. Apparently all we have to do is pray or watch our wife wash the dishes. Would be nice when your backup job could also buy you a house. The only helpful advice would be to workout, but again it is out of touch - “just go skiing and golfing in the same day!”. In this economy? Haha. Don’t worry guys just pray.. It’s like reading something from the Roman Empire likewise saying praying to Zeus or Apollo can solve your problems. Don’t trust the high reviews. 

Easier said than done method. Basic concept is to think practically about the actual probability of what you’re worrying about even happening.

Read the ebook for a class
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I really don’t like the way the book is written. Lots of fluff, not the way I learn. Outdated. 
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This was such a frustrating book to read.
1. Carnegie relies very heavily on anecdotal evidence. I usually like that in self-improvement books, provided that the author also includes scientific evidence to back it all up. Carnegie does not. Furthermore, a number of the examples he uses are unconvincing at best. I mean, being diagnosed with incurable illness/paralysis but being instantaneously healed through the power of Jesus and some cheerfulness? Sure, sure, I believe you.
2. This book did not age well. At all.
When it was first published, this sort of 'toughen up, people have it worse than you' talk probably would've been more than acceptable to say to people struggling with anxiety. Nowadays, it just highlights how little the author and the society at the time understood mental health.
A bit shocking, considering that Carnegie spends an entire chapter in the beginning talking about the importance of taking care of your psychological well-being.
3. It contradicts itself. I've already mentioned that Carnegie simultaneously recommends 'taking care of your mental health' and 'to stop being selfish and gain some perspective'. In addition to that he also heavily promotes christianity, and even flat-out says that without religion it's impossible to truly enjoy life/be a good person. Hell, for a whole chapter he would not shut up about religion. That is, after saying 'it's fine to be atheist, and I'll use an example of an atheist writer here just for you'. What?
4. Another quote that pissed me off essentially said: 'be nice and friendly. It's impossible to be sad and depressed when you're being friendly and smiling at strangers.' What kind of logic is that? I spend a day saying hello, how are you? to people on the street and my sadness and worries magically go away? There are so many accounts of the most gregarious personalities secretly being depressed and anxious. Take for instance the numerous comedians and actors who have struggled with depression.

These are the main criticisms I have, but there are many more. Carnegie should've stuck to the 'become a better businessman' type of writing/lecturing. He does NOT understand psychology. This book is literally his retelling of random stories he heard and read, coupled with old aphorisms.. It's essentially: "Mrs. A got better through the power of Jesus, Mr. B stopped being anxious because he remembered about the starving children in Africa and got ashamed" x100. There are a few good bits, don't get me wrong, but the majority of the book is just garbage.