A joke to illustrate the point:
Two guys are at the bar in a restaurant at the top of a sky scraper. One of the guys says to the other "Hey..... did you know that there's an air current that flows constantly at around the 10th floor of this building?? It's so strong that you can jump off the balcony here and it will carry you back up to the balcony!!"
The second guy is unimpressed: "Well I find THAT hard to believe! What do you think I am? Stupid or something??"
First guy: "I'll prove it to you.... come here, I'll show you!!" and with that the two guys go out to the balcony and the first one jumps off. Just as predicted, as the guy is plummetting to the ground, once he reaches the level of the 10th floor, he's suddenly swept away by the wind current and is lifted back to the balcony, safe and sound.
Second guy: "Oh my GAWD that is SOOOOOO COOL!! Damn, that's COOL! But how do you know it works every time??"
So the first guy jumps off the balcony, reaches the 10th floor again and gets swept back up to the balcony. He does it over and over and over..... every time the same thing happens. Finally, the second guy is totally impressed and convinced that it's completely safe. He jumps off the balcony and plummets to the ground...... SPLAT!! ..... street pizza.
The first guy is laughing his arse off and goes back into the bar. The bartender looks at him and says "You're mean bastard when you're drunk, Superman."