The Go-Giver uses the common business book trope of a salesman meeting with a "guru" to gain insight in ways to improve his career. Alas, the meetings do not help him to meet his original sales quota, but it does serve as the jumping point to his new career.The Go-Giver philosophy is basically "give and receive authentically". You must freely give to others without expecting anything in return. You should also let others give to you without making things to difficult. And finally, you should be true to yourself and not come across as fake. The values are anti-narcissistic, yet in the long run paradoxically helps benefit you. It makes personal and business life better as everybody is seeking to help others.
Messenger is the third and shortest book in the Giver Quartet. It follows more closely with the second book, and only superficially connects to the first and forth book. The series feels like two separate ones. Giver and Son go together, while Messenger and Gathering Blue are tied together. Had they been marketed as such, the reading experience would be much less frustrating.
The end of The Giver left many questions unanswered. You would think the sequel would fill in the blanks. Alas, in that you would be mistaken. (Try "Son", the fourth book in the series.) Instead, Gathering Blue takes us to a totally different area of the same "Giver" world. A young girl has a special gift, but also a physical abnormality. She is brought into the castle to serve with others. She learns that though she is treated well, she is also being "imprisoned" to have her talents used for the benefits of others. She eventually discovers her father and leaves. In some ways it is a repeat of the Giver, with a similar story arch in a very different community. Other than preparing us for the community of the fourth book, the second book is not critical in the Giver series.
Ninety Percent of Everything provides insight into the shipping industry. Today, it is often so cheap to ship things long distances that we think nothing of buying "cheap junk" from halfway around the world. However, things still need to travel across the ocean to get to us. The focus of the book is the ocean travel. The author spends time with a ship crew to experience shipping first hand. Crews typically come from less developed countries, where the wages from life at see can allow their family to live quite well back home. We also get plenty of coverage of the Somali pirates and possible reasons for their behavior. Alas, with the focus on the people at sea, there is not a whole lot of coverage of the whole logistics of the operation.
Unexpected "shocks" to the normal way of doing things can often help spark the creativity needed to accomplish something truly amazing. Messy opens with the story of a jazz pianist that was going to walk away from a performance due to the poor condition of the piano. However, as a special favor to the promoter, the pianist performed and produced one of the top performances of all time. The condition of the piano forced the pianist to improvise and go out of the "comfort zone" and produce something great.
After meandering around a few other side stories, the Giver series finally returns to the original story line in the conclusion. Son starts out in the same village as the Giver. We follow the story of a girl who became a birth mother. We gradually learn that she had lived at the same point in time as the Giver. She had a difficult birth and was then reassigned to a different job. However, in reassigning, they had forgotten to give her the "pills" that cut off emotion. She had the yearning to see her son, and eventually found him at the nurturing center. After he Jonas flees with baby Gabe, she ends up boarding a boat and ending up in another village. There she discovers a society vastly different from her own. (It somewhat resembles a somewhat primitive society with little technology, but a degree of learning and understanding.) From there, she builds up strength to climb out and find her son. Alas, she makes a great trade with the Trademaster and loses her youth in exchange for seeing him. She doesn't let him know until near the very end.