My brother says this is begging for the Heisenberg Uncertainty Principle, but that would ignore all my friends in the world of social sciences. Instead, the Observer Effect works just fine, which gets at the root of the issue.
UPDATE: Systemic MikeASchneider has alerted me to the similarities between this comic and one done by XKCD. No piracy was intended, and I maintain that this one is prettier and better kerned. While I’m a fan of XKCD, I can’t say I’ve read every one. Great minds think alike, I suppose? For those wondering where all the graphic design jokes have gone, stay tuned. They aren’t far off.