According to these folks, a petard is:
a medieval small bomb used to blow up gates and walls when breaching fortifications. In a typical implementation, it was commonly either a conical or rectangular metal object containing 5 or 6 pounds of gun powder, activated with a slow match used as a fuse. It was often placed either inside tunnels under walls, or directly upon gates. When placed inside a tunnel under a wall and exploded, large amounts of air would often be released from the tunnel, as the tunnel collapsed. By securing the device firmly to the gate, the shape of the device allows the concussive pressure of the blast to be applied entirely towards the destruction of the gate. Depending on design, a petard could be secured by propping it against the gate using beams as illustrated, or nailing it in place by way of a wooden board fixed to the end of the petard in advance.
As Shakespeare's Hamlet says in Act III, "For tis the sport to have the enginer Hoist with his own petard." Effectively, Hamlet turns the table on King Claudius [the engineer] at the expense of poor Rosencrantz and Guildenstern. See this site for an explanation of the relevant plot.
Today, to say "to hoist by one's own petard" is to say to be harmed by one's own plan. This came to my mind today when I read this article in the WaPo. In summary:
- The Mortgage Brokers Association bought a $100MM office building in the District last year,
- They're about to close on it,
- It's going to cost millions more,
- And they haven't signed any tenants.
Obviously, some would question the wisdom of carrying through with the purchase. In his defense, the MBA's president asserts, "Anytime is the best time to buy." Sure, you betcha. Or, as this fellow describes the MBA getting hoisted by its own petard:
"They are certainly getting what they deserve," said Dean Baker, co-director of the Center for Economic and Policy Research, a liberal research group. "Mortgage bankers encouraged people to take out mortgages that were very risky, and the result of that was a large number of the mortgages went bad and caused mortgage interest rates to soar. Now they are the victims of high mortgage rates and chaos in the market more generally."
Rosencrantz and Guildenstern are still dead.