"The signs of emergencies are varied and can be subtle. They may be apparent before or during the dive. A diver's ego or peer pressure may cause the diver to disguise a problem, such as a lack of competence, inadequate experience, overconfidence, anxiety, illness, or distress. Such problems may show up on the boat before anyone gets in the water. All divers should adopt the credo of the cave and technical diving communities: Any diver can call any dive for any reason at any time. No question are asked - and the credo applies before the dive even begins. All divers should agree to this as part of the predive briefing. If more divers felt comfortable not making a dive because it was beyond their experience, or they didn't feel well, or their karma was all wrong, or whatever, there would probably be fewer problems."
Excerpt from Scuba Diving Safety by Dan Orr and Eric Douglas
In the photo below, author Dan Orr does a book signing as part of the "Immerse Yourself Lecture Series" at the History of Diving Museum in Islamorada, Florida in 2015.