Chat between brother and sister:
-We have to go. Where's our grandmother?
-I don't know. She must have gone to play poker with her friends!
-Not again... Okay, let's find her. I'll go this way, and you go that way. If you find her, call me.
-Nice, we're quick to execute, and even if we don't find her, we already know which way not to go.

That's A/B Testing: comparing two variants and concluding which one is more effective.