like painting the Forth Bridge

Meaning

Prepositional phrase

• Never-ending; said of a task which will never be completed due to the perpetual cycle of having to recommence as soon as one has reached the end, or of efforts that are in vain because of this.

Origin

• Arising from the fact that the bridge across the Firth of Forth was in a continuous state of being painted (until finished in 2011, 122 years after its completion), because (owing to its large size) as soon as one end has been reached, it is time to begin all over again.