It feels like some books write themselves. This is not one of them.

It was a true challenge for us to translate the trillions of ideas we had in our minds. Our goal was a book combining a solid scientific background, readability, and practical advice. That combination is what makes the collaboration between us so unique. And it was this combination that we urged to see reflected in The Invisible Game.

First and foremost, we thank Frank Luby for helping us make it happen. His brilliance and skills in providing professional structure to what started as an unsorted collection of concepts and insights made the book both readable and solid at the same time. Without Frank, the book would not exist. It is as simple as that. Wishing him and his wife Sue all the best, we are deeply grateful for several years of intense collaboration.

We also thank the team supporting Frank: Ezra Blocker, who helped proofread the final drafts and Tauni Howes, who transcribed our initial working sessions when we began writing the book.

We thank Black Fish Tank, especially, and Luna Margherita Cardilli and Ljudmilla Socci for stepping in at the last minute to design the sticky notes as an integral part of the book. Since our first encounter, we enjoyed your inspiring creativity and were amazed to see your magic unfold.

We thank Annie Knight, Corissa Hollenbeck, and Purvi Patel, as well as the entire Wiley publication, marketing, and sales teams. From the day we first met, their positive energy and excitement became contagious and helped us through some difficult finishing pains. We thank Premkumar Narayanan for help with proofreading. Special thanks go out to Danilo Zatta for the initial spark and introduction to Wiley.

We would like to thank Arnold van der Beek, Gaby's first-ever sales boss. As one of the best salespeople Gaby has ever met, he became a proof-of-principle reader and trusted consultant for our practical advice. Throughout her extended sales career, Gaby has worked with many teams on both sides of the negotiation table who somehow have all contributed to this book in one way or another. Unfortunately, they cannot be all named here. Representing many others, special thanks go out to Jeremy Celliers, Felix Frowein, Scott Violette and Elisabetta Soana, Gerardo Enriquez and Renaud Joly, Jean-Sebastien Degrange and Mark Haward, Cecile Seguy and Celine Maggia, Nils Mader, Clara Tri, and Javier Acosta.

We are grateful to Viktor Stebner, Tobias Hahn, Julia Kästle, Janine Rau, and Sara Bertsch for insightful comments and suggestions on previous versions of this manuscript. Also, Viktoria Frese gave us thoughtful feedback and helped us organize our reference database.

And we thank our families for their support and patience when we spent endless hours on video conferences with each other or with Frank.

Gaby: I thank my sister and my brother and their families so close to my heart for their love and encouragement, and in particular Peter, my husband and love of my life, for his inspiration, practical advice and humour. Joy and love are the key ingredients of happiness, and each morning I wake up to days full of both.

Kai: I thank my wife Katja for all her love as well as her acceptance of and patience with my crazy writing schedules – it is fabulous to have all that backing. Of course, I thank Lina and Karlotta for the daily dose of sunshine and happiness they bring to our lives. Finally, thanks to every one of the Müller and Holderle families for all the constant support.