I had to import data from Excel documents into MS SQL Server. Since this was supposed to be a one time thing I used the import wizard. Some values where quietly

I had to import data from Excel documents into MS SQL Server. Since this was supposed to be a one time thing I used the import wizard. Some values where quietly ignored because the cells happened to have different formats than the surrounding cells. They looked exactly the same, so it took me a little while to figure it out. And if I wouldn't have done some simple sanity checks those errors would definitely not have been discovered before it was too late.