We stood at the edge of the lake.

Everyone was in a wetsuit.

Except for me.

Wetsuits: hundreds of people.

Boardshorts: one person.

"You're brave," another triathlete said.

I shrugged.

I was not brave.

I was dumb.

I did not think this through.

If I had done any research, I would have learned that the lake was 50 degrees.

If I had done any research, I would have learned that in 50 degree water, hypothermia sets in at 30 minutes.

I had one minute to think of a model and make a plan before the starter's gun went off.

I've got it, I thought.

When I move, my body generates heat.

The cold will be painful.

Start slow.

Swimming will make me hot.

Then swim the second half faster.

POWWW.

The gun boomed and hundreds of wetsuits dove in the water.

I dove in last, in my boardshorts, and started swimming slowly.

I am typing this story eleven years later. In warm clothes.

And yet, I just felt shivers.

As I learned that day, my model of the world was bad.

Swimming generates heat, but in water that cold, you lose heat 10x faster than you make it.

Back in Lake Berryessa, things were not going as planned.

At the halfway buoy, I was struggling to control my limbs.

My teeth were chattering uncontrollably.

The only thing I had going for me was that my wiser, wetsuit-wearing friend Tom had slowed down, to make sure I stayed alive.

Knowing Tom was there to keep me from drowning, I flapped on.

After half an hour, I made it back to shore.

I had never been so cold.

I was shaking so bad that it took me twelve attempts to lift my leg over my bikeseat for the next part of the race.

But...

I was alive!

And I had learned an important lesson.

Bad models of the world can be dangerous.