I thought this would be fun (and educational).

Mysteries:
a) If you include two asm files with different filenames but identical NAME statements using Keil you get 'not found' for everything in one of the files. You check your libray commands and whatever for a good while till you by accident discover the reason.
b) Once I knew that something was wrong in a CPLD, although the simulation was fine. I scoped and scoped and did not see anything. Finally with some thought I reasoned that for the problem to exist there had to be a glitch at a certain place. The scope showed nothing so I scoped and scoped all over the place. Finally I said to myself "It has to be there" and changed the CPLD file and everything started to work. I then borrowed someones 'superscope' and, indeed there was a barely noticeable spike that neither my scope or the simulator could 'see'

great goofs:
a) I have twice mixed !RD and !WR pins on a sram (make sure you never copy a file with a bug)
b) I made a base schematic for a machine control and used it many times as a base for schematics with great succes. Then I 'missed' that the motor for one job was 230V and left the 400V input on the schematic, POOF.
c) A schematic I once made (more than 2000 component pins was perfect EXCEPT I had forgotten to include the oscillator!

Erik