I’ve always had this theory in my head: that no matter what we do, we always do what comes easiest. In other words, humans always follow the path of least resistance.
Imagine there are two cups in front of you. The first cup contains plain water. The second contains urine (stinky, dirty, horrible, horrible urine). I ask you to pick a cup to drink from (and you, being a very compliant person, will follow everything I tell you to do). The obvious choice would be to drink from the first cup, the one containing plain water.
But if I told you that unless you drank from the second cup, your loved one would be tortured and then killed, would you still drink from the first cup? By setting this condition, I effectively increase the resistance to your drinking of the first cup tremendously — and you would probably be much more willing to drink from the second cup than you were before.
The drowning man
Now, imagine you an average swimmer — able to swim, albeit not as well as a life-guard. As you walk through a park, you hear screaming. As you turn, you notice a man struggling frantically in the water, obviously drowning and in need of help. You, being a not-so-good swimmer, first look around to see if there were other potential life-saving candidates. Being a very early monday morning, you see no one else around.
You now have to decide whether or not to jump in to attempt to save the drowning man. Your life-preserving instinct tells you that you are not a good enough swimmer, and that if you jump in, you would most likely accompany the victim into the after-life. Your herd-instinct however, tells you that you should help — if you refuse to help, would you be able to live with your conscience?
Stuck between a rock and a hard place, your next action, to jump in to help or not, will be determined by whichever action is easier for you. If you were determined to preserve your life at all costs, and were willing to fork out the price of a guilty conscience (possibly throughout your whole life), then you would let him be.
If you were unwilling to pay that price, and would rather die trying to save him than live with the guilt, you would jump in. Either way, you go the path of least resistance.