The new engineer approached the old engineer.
The new engineer asked: "When things go wrong, who fixes it right away?"
"The brave soul who is on-call," said the old engineer.
"And after that, what happens?"
"We take some time and give it another fix that lasts for a while," said the old one.
"Yes," said the new engineer. "But who will fix it permanently?"
"Mu," the old one said.