The water was opaque, its surface calm and tinted silver by a typically silver Otways sky. Four of us had started swimming together, but two had swum ahead to the pier. Joni and I had turned back to the beach from the pumping station and had been swimming for 10 minutes and just passed the red-roofed house, the point at which, one friend says, you know you’ll make it back to land. We were out wide in the water because a rip was running along the rocks.

I was ahead and Joni about 10 metres behind when a big shark swam fast beneath me going from my head to my toes, towards Joni. The word “f---” has risen through the ranks of English etymology to become the “Good God” and “Allahu Akbar” of the godless. It is simultaneously an exclamation and entreaty, a proclamation and a prayer. I shouted it into the water and acoustic morsels of the word bubbled up either side of my face.

I recall asking myself, “What’s to be done about this?” Turns out it was a pointless question, because I acted before answering. Without stopping to tell Joni we were being eaten, I abandoned her. I started to pull for shore with the adrenal zing of a wounded kipper.

Flight or fight? Mystery resolved, question answered – I’m a flight guy. I smelt the great white’s blubbery breath, and it was bon voyage. Arrivederci, Joni. But my flight only lasted for about five strokes, until I realised there was nothing dangerous out here I could outswim. My retreat could only manifest as a kind of ham-fisted foreplay to any predator. Best not to behave like prey.

I stopped and flipped up my goggles and looked around and found we were amid the rollercoasting dorsals of dolphins. Those piebald frauds were smiling as implacably as Albanese selling bunkum. But if this was their first contact with humans it was as unhappy as Cook’s with the Māori, because I denounced them roundly until they vanished.

Why does a sudden dolphin always look like a shark and a sudden shark never look like a dolphin? It’s because doom is a jester and fear keeps us alive. The only reason I’m here is that a long line of Camerons have been, if not cowardly, then wisely less brave than those around them.

When we got to the beach I’d settled down, and Joni and I marvelled at having swum with dolphins, because dolphins, when they’re identified and certified as dolphins and not masquerading as nightmares, are mystical, otherworldly creatures. We spangled and fizzed with the kind of Thoreauvian epiphany you’d pay big money for at a Queensland water world. And I was confident Joni didn’t know, and would never know, of my brief, aborted, desertion of her. (She doesn’t read The Age.)

I told myself I hadn’t abandoned her. I told myself that even if I could outswim Jaws I wouldn’t have kept churning towards shore, leaving Joni as the proverbial hindmost which the devil let take. No. I’d have waited bravely alongside Joni in that bay of gilled ghouls, halving her risk.

The military takes years to train soldiers to ignore the impulse for self-preservation. (A discipline neglected by the French prior to WWII, leading to astounded villagers often witnessing the Armee De Terre attacking and retreating simultaneously.)

We all tell ourselves a story of how we would behave when the siren blares, the bomb goes off, or the tusker charges. And given society’s expectations, perhaps it’s psychologically crucial to the wellbeing of men that they grant themselves honorable behaviour in the imagined emergencies of the future. We have a salutary, but perhaps false, licence to believe we will act with courage.

For my part, I have defeated a thousand machete-wielding home-invaders with a tire iron while drifting off to sleep. But, until a dolphin runs the experiment on us, none of us really know how we will behave when the doom bell is rung.

In the movie Downhill, Will Ferrell abandons his wife and kids as an avalanche bears down on the family. The snow stops short and they are spared. But his behaviour is incontrovertible testament to the value he puts on his own and their lives and he is debunked as father and protector.

Of course, Joni is neither my wife, nor child – merely a friend. Our circumstance is more analogous to that of George Costanza and the children he abandoned at a birthday party when a house fire broke out.