If skydiving were safe, the parachute center would not require you to sign a waiver.
Do not collaborate with someone you would not go camping with.
Book writing is not a get-rich-quick scheme. Anyone who decides to write a book must expect to invest a lot of time and effort without any guarantee of success. Books do not write themselves and they do not sell themselves. Authors write and promote their books.
Marriage is the only game where the trapped animal has to buy the license.
Write on a subject you love. Your profit center should also be your passion center.
If the big publishers are doing so well, why do they require writers to send return postage with their manuscripts?