The meaning of the expression "on the bubble" is about being on the threshold; it is focused on the fine balance between success and failure. It is the last or among the last to qualify for the last competitive position(s) in a competition such as a car race or a spot for a place on a professional team roster.

This U.S. expression seems to have originated in the car racing community. In particular, it is the aficionados of the Indianapolis 500 race. The first citation or use of the expression can be found in a report on the 1970 running of that race. The Lima News, May 1970 stated:

"On the 'bubble' is rookie Steve Krisiloff whose 162.448 m.p.h. was the slowest qualifying speed last weekend. With only six spots open, Krisiloff's auto racing machine would be ousted if seven cars qualified at a faster speed this weekend."

The qualifying event at Indianapolis is now known as 'Bump Day' or 'Bubble Day'.

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