Drawing a Blank
Failing to recall a memory; unable to remember something.

If someone is incapable of remembering something, then the common idiom Drawing a Blank is a saying that might be used to describe the forgetfulness.
My Thoughts

Hmm, I can't seem to recall what I wanted to say here. It was something about how this expression... yeah I don't remember, sorry.

Phrase Origins

This idiom may have stemmed from the lottery from hundreds of years ago. Contrary to how it's used today, the phrase back then had an entirely different meaning behind it.

According to ThePhraseFinder, during the 16th century, people wanting to take part in certain lotteries would write their names down on a ticket and have it included in a pot. Notes with prizes written on them were then added to a different pot, but some of them were left blank. Afterwards, both a ticket and a note were drawn from their respective pots, and a winner was announced. There was a chance, however, that a person drew a blank note, resulting in them winning the prize of nothing.

At some point in history, the meaning of this saying went from coming up short in the lottery, to a more broader usage, where we sometimes come up short in remembering things in general.

Common Phrase Meanings and Origins > Drawing a Blank
Examples of The Phrase Being Used

"Yeah, I remember you from high school, you were that, uh, sorry what was your name again? I'm drawing a blank here."

"Mark could only draw blanks as he desperately tried to remember his cell phone number for a curious friend.
Note: For most popular sayings and other common phrases you come across on this site, finding the precise phrase origin is difficult. What's provided is around the earliest known date the expression was being used in.

Usually the expression comes from a quote found in an old newspaper, book, poem, or play. However, if the idiomatic phrase is already being used in one of those, it's likely already a well known saying, thus it should be assumed the origins are older.

There are rare cases where determining an idiom's origin is possible. Anyways, for the most part, you'll get a rough idea on how long ago certain phrases were being commonly used in, and you can get a rough idea on their age.
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The meaning of the phrase Drawing a blank.
The origin of the saying drawing a blank.
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