Comment by Optimal_Persona

Haha, I discovered "always TRIM both leading and trailing spaces on both lookup criteria cells and source tables" the hard way too. At 3 in the morning...All of the 20-hour days/nights I've done as a data analyst were due to Excel malfeasance.

Also - 15 digit NUMBER precision leading to truncated values that you only discover when it's too late; no Macro undo; no way I'm aware of to transform columns/rows from formulas to their values without intermediate cut/paste steps; lots of essential features (like "Copy only visible range containing hidden cells") buried in Find & Select > Go To Special menu without keyboard shortcuts; Excel's magic ability to change cell data types by merely touching a CSV (open/closing without saving changes)...