In summary, it's a trope filled self help book, I doubt the truth of many of their "totally crazy things we did" stories (see example at the end of review), and the stories they hold up as examples to live by are in fact dangerous mistakes that the reader should learn NOT to repeat.
This book starts of "OK" and then goes downhill. It falls into numerous self-help tropes including numbering and naming object lessons. One chapter is about the "5 life stories" and then "the 6 mirrors." This kind of tired self-help object lesson pandering is interspersed with interesting stories from the authors' lives. These stories are initially inspiring and back up their urge to "whenever possible, make 'someday' today."
However, as the book continues these stories devolve into cautionary tales about why this can turn out to be a terrible philosophy. Several stories illustrate the extreme ends of how "push your limits" can be harmful. Yet, these stories are not held up as warnings, but rather as encouragement.
As an example Tim tells a story about how he took the high school cross-country team he coached on a foolish run up a mountain in the dead of winter with no thermal gear or water. This resulted in 2 team members getting lost late at night, one of whom became too hypothermic to even shiver and who may have died had he not been discovered, completely by chance, by a group of hikers as he wandered off the trail. Another runner became delirious on top of the mountain and began removing his clothes and yelling at the sky. Tim concludes this story by recounting that the team "lived more in a single day and discovered more about themselves than some people do in a lifetime" and "by taking the initiative to get out the door...lived a story they will one day be telling their grandchildren."
Three team members could have legitimately died by Tim's own account and no member of the team was remotely prepared for the undertaking. It was a stupid, foolish, dangerous thing to do that only turned out okay because they got lucky. This isn't the kind of inspiration anyone should be following.
As a further point, as I read through the book I became less and less convinced of the author's relationship with the facts. Another "inspirational" story they tell is about deciding to ride their bikes 55 miles north to Fort Collins, despite one of them not having a bike and the other having an old one he hadn't ridden in 3 years. The authors claim they borrowed a bike and made the ride on rusty mountain bikes that left them blistered and hurting. They then challenged each other to complete the return ride in under 3 hours or else do it a third time the next day. Then, the next day they ran a 10 mile training run before getting on the bikes to ride home. They claim they then raced home and finished in 2:52:00, just in time to not need to repeat the challenge.
That works out to a 19.2 mph pace assuming no stops of any kind, which is difficult to believe considering they were riding with traffic on normal roads. By comparison, the average finish time for the bike leg of the Ironman 70.3 race (56 miles) for EVERY age group (excepting professional racers) is slower than this pace. [runtri website]
So, they claim that, completely untrained on a bike, using old mountain bikes not fit for them, after having ridden 55 miles the day before, and after having ran 10 miles that morning, they completed a Half Ironman racing bike distance faster than the vast majority of Ironman athletes do after having spent months training for the event and weeks tapering down to that specific race who are riding road and racing bikes fit to them... Yeah...BS.