More accurately,
2-Jan
Why the most useless date format is the default is another question
For a program that was created to work with numbers, Excel is absolutely horrendous at formatting them. 164849398282 by default turns into scientific notation like 163748e+3, you convert it to a number and half the time it gets truncated and turned into zeroes at the end. So you get lucky one time and it converts over cleanly, you save it, and open the file again and it’s back in the old useless format. Or when your number starts with a zero. You try putting a zero before, convert to text and pray it stays.
Or the times there’s a number in a cell and it doesn’t recognize it as a number even if you try converting it to a number, currency, or anything else. So you can’t sum it or use it in any formula. But once you double click on the cell, the number magically awakens, aligns itself to the right, and is suddenly recognized as a valid number.
I’m sure there are ways to solve the issues mentioned above, but typically the solution is tedious, unintuitive hacks.