At the top of every Excel financial model I built was a cell I hoped never to see.

ERROR.

In my twenties, I worked at a private equity firm in New York City. The hours were brutal. A hundred-hour week meant actually sitting in the office for 100 hours.

Most of that time was spent building financial models in Excel. Income statement. Balance sheet. Cash flow. Five-year forecasts. Leveraged buyouts.

When I started, I understood each piece individually. What I didn’t understand was how tightly everything was connected.

Change revenue and net income changes. That changes retained earnings and cash. Cash changes how much debt you can repay. Debt changes interest expense. And interest expense flows right back into net income.

Pull one thread and everything moves.

The guy who trained me had a simple trick for keeping us honest. At the top of every model, he built a cell that flashed ERROR whenever the balance sheet didn’t balance.

You’d change revenue but forget working capital. Add capital expenditures but miss depreciation. Pay down debt but forget to change interest expense.

ERROR.

Eventually, I stopped needing the cell as much. I understood the model well enough that when something was wrong, I could sense where to look.

Running is like that.

Add mileage and recovery has to change. Cut calories and workouts suffer. Stack hard sessions together and your long run goes flat. Sleep poorly and suddenly a pace that felt easy last week feels impossible. When you’re new to training, these connections can feel random. After enough years, you start seeing the model. There’s no red ERROR cell flashing in your training log. Your body gives you something subtler.

I think the trick is understanding your system well enough to notice when something stops balancing.

What’s the first sign your training is out of balance? Hit reply and tell me.

Happy running!

George