You are the only human alive that I have ever heard use that phrase other than my Grandmother and Mom.
I never understood it as a kid.
Who is this Katy and why is she barring the door?
Katy was hardcore man, she barred the door with her arm to save the king. Didn't work, but she gave her all (and her arm).
Then the Queen cried, "Catherine, keep the door,
And I to this will suffice!"
At her word I rose all dazed to my feet,
And my heart was fire and ice.
...
Like iron felt my arm, as through
The staple I made it pass:-
Alack! it was flesh and bone - no more!
'Twas Catherine Douglas sprang to the door,
But I fell back Kate Barlass.