Stress
The SCUBA instructor stressors are lining up faster than we can talk about them, so let's get going.
First, let's say you're teaching an Open Water Diver classroom session. You're discussing the physics of diving, how the body responds to pressure changes, yada, yada, yada. No, it's not the most exciting material, but it's the foundation of the course and everyone's got to learn it.
Although most of the students look reasonably alert, you've got one guy in the back who is clearly zoned out. He's staring blankly at either you or the white board, which is odd since you haven't written on it. Either he's got some ear wax buildup or he was out way too late last night. Tough beans, though, since he's still got to pass the written test to get his C-card.
Then you've got the Open Water student who's afraid to put her face in the water. Yes, she passed the swim test, using the sidestroke and backstroke, and she seems physically fit for diving. She also aced the classroom session. When you get to the pool and start practicing the mask and snorkel work, though, she freezes in place and won't continue.
Clearly, you've got a problem. The lady's got to practice and demonstrate her underwater skills to get her certification, but she won't go underwater. You've also got fourteen other students to teach and monitor. Stress level up yet?
Well, this situation should put you over the edge. You've gotten everyone to their four certification dives, which represent the final hurdle before a student gets his or her C-card. We won't comment on the fate of the poor woman who wouldn't go underwater. Let's just say you've taken the students to a nice dive spot just off the Florida Keys, and you and your instructor pal have carefully evaluated everyone's dive skills over the last hour or two. All the students have passed with flying colors.
You've given the "thumbs up" to return to the surface, and heads start popping up within a fifty-foot radius of the boat's "Diver Down" flag. You count, and count again. Then your instructor friend counts, and you get a sinking feeling in your stomach. You're one diver short. The guy's buddy is here, but there's no sign of Scott, the class clown. Has he decided to push the limits of his newfound freedom, or has something gone really wrong? Good thing you're wet anyway; no one can see you sweat.