The spreadsheet is the best tool in the world until it isn't. It starts by solving things and, at some point, becomes the problem: parallel versions, formulas no one understands, data only one person knows how to update.

Some signs are clear. When the same information is typed in two places. When closing the month depends on an all-nighter. When one person on vacation blocks an entire process. When no one trusts the number without checking the source.

None of these signs call for "one more tab". They call for a system designed from the real process. That is the point where the operation has outgrown the spreadsheet, and staying on it starts to cost dearly.