My son Andrew is three years old. Three is a fun age. As a rule I try to simply watch and enjoy; I’m told that these years will spin by fast so I am making an effort to pay attention and notice the details.

Andrew likes routines and patterns, as do most kids his age. Our bedtime routine is a standard, unvarying series of activities – disrobing, placing his shoes, selecting pajamas – that winds his little three year old brain down to a state where it is ready to absorb a bed time story, climb into bed, and go to sleep.

Part of his routine is brushing his teeth. Immediately after putting on his pajamas I sing (to the tune of Mary had a Little Lamb) “Now it’s time to...” and he responds “...brush the teeth!” Then he brushes his teeth. Seven notes, total. We do this every night. But a couple of days ago I sang my opening line, and instead of immediately popping off with his line as he usually does he paused for a second, and then responded with “...wash the hands!”

This, to Andrew, was the funniest thing that anyone had ever said, and he cracked up with peals of genuine laughter. Not the giddy, hysterical laughter that you get when you tickle him. This was a belly laugh; a “damn that was funny” laugh. The boy had cracked himself up. He’d pulled the old switcheroo, the change-up. He’d yanked the rug out from under daddy’s expectation. Funny!

Now as jokes go this wasn’t a particularly funny one. It hardly a joke at all, really. But a couple of things really caught my attention about the episode. First, of course, was his reaction, which in itself was funny. It’s hard to watch a kid laugh and not laugh yourself, especially when the kid in question is your son.

But the thing that really got me was the fact that, at that very moment, I saw him come up with the concept of humor. Andrew invented the joke. He’d never told a joke before, and to my knowledge he’d never heard one that he understood. The fact that comedians have been telling jokes since the dawn of man is irrelevant. He didn’t plagiarize their work; his little brain came up with this concept on his own. The joke! Funny!

Of course there’s nothing special about my kid in this regard; every kid goes through this, I imagine. But as I watch it unfold in my own son it dawns on me how little original thinking I do. Over the course of the day I normally do very little real thinking at all. Like most of us I travel the well worn grooves and patterns of my life, and rarely encounter a situation that requires a response outside of the reflex reaction which has been conditioned over my lifetime of accumulated experiences. Rarely do I have to figure anything out; I can get through the average day without making any real decisions. At forty years old my predefined prejudices, expectations and habits are so ingrained that there is a pre-determined response to all of the myriad forks in the road I encounter on a daily basis. Every now and then a novel problem pops up, but as a rule life doesn’t require a lot of thought.

But a kid? Now that’s a different story. Kids are operating with a blank slate. They’re filling that slate at a breakneck pace, but early in the game they’re still figuring out the rules. The computer in Andrew’s head has a blazing fast processor but the hard drive is empty. When Andrew is in the park and encounters a big duck he doesn’t know whether a) it will be friendly or b) it will charge him and try to take the cracker he’s waving around in his fist. So he has to stop and consider everything. Eventually he’ll accumulate enough experience to know intuitively which ducks will wait for him to toss the cracker and which ones will try to knock him down, but for now a lot of thinking is required. He has to try to interpret the duck’s body language and extrapolate this to predict the animal’s intention and probable course of action. He has to think!  Often, getting it wrong teaches him more than getting it right.

There is an appeal to looking at the world through a child’s eyes, but I’m not going to try to jettison all of my accumulated rules and patterns; I would not be able to function as an adult without them. But watching my son I am reminded that it is useful to at least be mindful of my prejudices, and allow that mindfulness to prompt me to challenge some of my assumptions.

This is particularly important for investors, for whom mental models are particularly strongly imbedded by the non-ambiguous feedback of winning and losing money. Some of the turbulence in today’s market we’ve seen before, and remembering the past will help us prepare for the future. But not always. Good investors have to question which features of the market simply part of the economy’s cyclical nature, and which represent fundamental shifts, and therefore require us to consider new paradigms. In short, it reminds me that good investors can’t rely exclusively on experience; they have to think.

I’m lucky to have someone to remind me of this. I just hope his jokes get better.