" There's a limit to the power of a spring, no matter how tightly one winds it.'
'Oh, yes. Yes. And you hope that if you wind a spring one way, all its energies will unwind the other way. And sometimes you have to wind the spring as tight as it will go,' said Vetinari, 'and pray it doesn't break.'
His expression changed.

'Oh dear,' he said. 'He didn't thump the wall. I may have gone too far. "

― Terry Pratchett , Men at Arms (Discworld, #15; City Watch #2)