My first week as a finance intern, I built what I thought was a solid cash flow model in Excel. Nested formulas, colour-coded tabs, the works. By Thursday my supervisor pointed out a circular reference I had missed, and the numbers I had presented to the team were off by nearly $40,000.
What went wrong
Excel does not validate your logic. It runs whatever formula you give it, even a broken one. I had no version control, no audit trail, and no way to quickly isolate where the error started. A dedicated tool like Adaptive Insights or even a structured template in Google Sheets with locked formula ranges would have caught that much sooner.
The lesson that stuck
The problem was not Excel itself. The problem was using a blank workbook as if it were a proper financial analysis environment. Tools like Cube or Planful exist specifically because freeform spreadsheets are fragile under real working conditions.
If you are just getting started, pick one tool and learn its constraints before building anything you plan to share. Knowing what a tool cannot do is just as useful as knowing what it can. That internship taught me to read the documentation before I open a new file.