Common Wisdom?

Sunday, it rained. Monday, the rain turned to snow. Tuesday, my morning commute was fifteen miles of slow 'n' go on greasy glass, all the while fighting my Jeep Cherokee's tendancy to break the rear wheels loose and spin out. Near the junction with Highway 52, the lady in the shiny new Jeep Liberty on my port quarter failed to learn from my example and spun out across three lanes, narrowly missing both me in the right lane and the semi in the far left lane, but getting t-boned on the rebound by the Taurus in the center lane.

For some reason, this got me thinking: what are the things that we all know must be true, because we've seen 'em a zillion times in books and movies, and yet clearly aren't? The first one seemed strangely obvious to me: Jeeps get good traction. Only on dirt or mud, I'm afraid. On snow and ice, they're worse than my old Bonneville.

Okay, that's a start. But what else comes to mind? I thought of some books I've read and movies I've watched recently, and came up with:

Hookers often have hearts of gold. No, the correct answer is "chlamydia and crack habits."

If your situation seems hopeless and you're out of ideas, a brilliant inspiration will come to you if you get falling-down drunk. I can see how that one would seem credible to a Hollywood screenwriter, but...

It was a slow commute; I came up with lots more. But what's your favorite example of common wisdom that just ain't so?