Normally, you cannot take something without paying for it. Such an act would normally constituted a theft. Imagine, though, that you see a man in need of immediate medical attention laying in the road. You realize seconds matter in this case. You see a convenience store and your instincts kick in. You run in to grab gauze and water and run out without paying for it to go help the man. Theft? Certainly not. You have the defense of duress or necessity. But you might have to do some proving before the charges get dropped (that is, if you are charged in the first place).
Before a jury can find that you acted under the defense of duress or necessity, they must find the following six elements:
The reasonableness of your belief that a danger or emergency existed will be examined in the light of all the evidence that surrounded you at the time.
If the jury believes that you committed the crime out of duress or necessity, you should be found not guilty.