before {sb} (can|could) say Jack Robinson

so suddenly or quickly that leaves one with no time to react or notice anything

The exact origin of the idiom "before someone can say Jack Robinson" is uncertain, but it has been in use since at least the 18th century. It is believed to have emerged in England and is often employed in storytelling, anecdotes, or casual conversations to describe instances where something happens rapidly or unexpectedly.

They react to changes before you can say Jack Robinson, adapting instantly to new circumstances.
He finished the race before you could say Jack Robinson, crossing the finish line in a flash.
They resolved the issue before anyone could say Jack Robinson, finding a quick and effective solution.
The cheetah sprinted faster than anyone could say Jack Robinson, leaving everyone in awe of its speed.
The internet can deliver information quicker than you can say Jack Robinson, providing instant access to knowledge.