I remember Happy Days where Fonzie (Henry Winkler) was so macho he couldn’t say “I was wrong.”

When I’m trying to figure out why something is wrong, it’s easier to blame someone else. Usually, my first guess is not “It’s my fault.” However, I’ve learned that if I’m programming and I think it’s a compiler bug, I’m probably wrong.

I have a spreadsheet of driving statistics from 2003 to 2017. I was cleaning house this month, looking for old documents to scan before I shredded them. I was pleasantly surprised to find a few months of gas receipts from 2010 that weren’t in the spreadsheet. Score!

I entered the data and wanted to include it in my summary table showing each year’s totals.

I got a new row for 2010 set up. But 2010 had $0.00 spent and 0.000 gallons and wouldn’t show what I expected. It was very frustrating. I was trying to force Excel to do-the-right-thing and calculate those values and it refused to. Matrix formulas were a new to me, so I thought it must be some subtle Excel flaw. (Thinking along the lines of it’s someone else’s fault.)

I was getting pretty frustrated until I looked at my table a little closer. All of the other rows had the beginning date on the right and the ending date to the left, backwards!

When I added a 2010 row, I had entered the dates normally. Oops! I was wrong. Rather than kick myself, I just swapped the dates.

It wasn’t a (figurative) compiler bug after all nor someone else’s fault. I wonder how often I make equivalent assumptions in real life?

After trying to tell myself the backwards columns were too much work to fix, I noticed how much time I had already wasted because they were wrong. It turns out, Excel is smart and it was trivial to fix.

(The 2010 receipts didn’t have mileage and the table shows zeros for that data.)