A shark attack is sudden, visceral and overwhelming.
And it's impossible to be a tough guy in the face of one.
The sheer terror of it overwhelms us, paralyzing us, helpless to do a thing about it.
And, most important, and easily overlooked:
Shark attacks are astonishingly rare.
It turns out that there's no useful correlation between the enormity of a hazard and its relevance to our lives.
The same thing is true of your project, your upcoming speech, and the meeting you're about to schedule.
Using the phrase, "shark attack" to describe the imaginary but horrible pitfall ahead is a good way to remind ourselves to focus on something else. Better to prepare for a hazard both likely and avoidable instead.