Once you are good at something, everything feels so easy. Just like riding bikes and driving a car, you know what to do without even thinking about it. The feel of ease when working with a model is what I call intuitive.
When I first started my career, it is fascinating to watch my boss take a glance of a model and tell me what is wrong. Sometimes he would open one of his text books and show me an equation to explain the theory behind it.
He had a PhD in hydraulics and had been in the field for more than 30 years, so I reasoned, a PhD and many many years of experience might be what it takes to do something like that.
In the following years, I tried many different things to be like him. First I tried what I thought PhDs would do, reading papers and solving differential equations. After reading and re-reading my college text books and trying to memorize the differential equations, I didn’t get anywhere. Then I just gave up on that.
Only much later, I noticed that sometimes I could tell things that are not right about a model just by glancing at it. Since I still have no clue how to solve differential equations, I am pretty sure it is not the math that helped me. So what helped?
Since it feels so easy, it cannot be something that I have to calculate using math. There must be a trick that I used to “cheat” on it. As I reflected, I think it must be these simple and weird mental maps I put together in my mind that helped.
I might not know how water is supposed to flow through pipes, but I know very well how cars moving along a street.
If I have a small car, a truck and a minivan entering a one way tunnel on one end, I can be 100% sure, that I’ll see the same cars in the same order going out of the tunnel at the other end. And that is my first mental map for how water moves through pipes, it comes out the way it comes in.
The important thing is that the mental map needs to be super easy to apply and it only needs to be right when something is terribly wrong at the very beginning. The key is to get into the habit of guessing what the modeling results should look like without too much thinking, once you get into doing something like this, every time you look at a model, you practice your skills.
Very quickly I noticed my mental map is flawed, because after the water goes out of a few long pipes, its peak starts to lower, and the shape of the hydrograph starts to “melt”. So I need to devise a better mental map for that, it reminds me when getting stuck in traffic, when the cars are moving, they are not moving at the same time. It will take a while when you see the cars way head of you moves before it is your turn to move.
So I reasoned that water works in a similar way, when the high flow reached the pipe, it caused a traffic jam, and the water ahead of it needs to move out before it can move, and that will have the effect of a melting shape.
As you can see, nothing here is scientific, and I bet my hydraulic professor will be so disappointed to read this article.
However, as someone who worked on models for decades, all these silly mental maps never failed me, and they are still serving me very well.
Most of us mistakenly thought the way we learn things is in a classroom setting. Time and time again, I found that is not true. What get me through out my day at work are these “mindless” judgements I made at a snap second, I only use the logical part of my brain working on very complicated tasks, and that only happens perhaps an hour or two of the day, and they are very exhausting, there is no way I can do that full time.
So here is my advice for anyone who prefers a more intuitive way of modeling. Come up with simple and silly mental maps for how the model suppose to work, and apply every time you look at a model, and before you know it, everything will start to feel much easier.
