@ethanschoonover #3 must include a section on How Do I Know This Is Right?, techniques for explaining and verifying spreadsheet results. This is the same expectation we have for both manual calculations and traditional computer languages and it absolutely must be extended to spreadsheets.

The biggest problem I see is not with spreadsheets in general but with Excel in particular. Excel makes error detection, documentation, and verification virtually impossible while adding in the risks of unintentional type conversion and silent precision loss. I could probably spend a month on all the ways Excel is impossible to trust for anything you consider important.

When cooking for others, you have a responsibility to use clean cookware and keep food at a safe temperature. You have similar responsibilities when calculating for others regardless of the tools you use.