I had to give a presentation to the CEO about the new product we are developing. I was very nervous. He asked me simple questions which I could normally answer with no problems, but because of my nerves I drew a blank (sich nicht erinnern können). It really looked like I had no idea what I was talking about.
Queen Elisabeth I, needing money to run the country, established a national lottery in 1567. The lottery worked by putting tickets with the participant’s names into a ‚lot pot‘. An equal number of notes, some with the prizes written on them and some blank, went into another pot. Pairs of tickets were chosen (or „drawn“ – „to draw“ had a similar meaning to the word „to pull“) from the two pots, matching a person to a prize. If you drew a blank, you didn’t win a prize. So the idiom came to mean „not having enough luck“.
In modern usage, draw a blank more commonly means to fail to remember something, though the older meaning is still in use.