Analogies
Talking with Foxtrot on IM just now, I ended up with the mental image of trying to survive a bazooka by choosing between defending yourself with a feather or waiting for a mail-order baseball. If you know Foxtrot, then it should be obvious by now that we were discussing the options of defense against an Earth-impacting asteroid or comet. The feather is military nukes aboard ICBMs, while the baseball that doesn't yet exist is some other NASA plan that actually has a chance of working.