Jeopardy
In addition to ability and opportunity, the criterion jeopardy requires that, in your specific situation, a reasonable and prudent person would believe that the existing threat of death or great bodily harm is indeed a real threat and is immediate and otherwise unavoidable. The jeopardy test is what helps us separate real threats from potential threats or imagined threats. A large part of the jeopardy test comes down to the context of a given situation.
Walking through the mall, nearly anyone could punch, stab or shoot you but what is the likelihood and why would someone do that? The reason you are not actively "defending" yourself as you move through the mall is because you have no real reason to believe that you are about to be violently attacked. Context is helpful in understanding the nature of threatening or potentially threatening situations.
While you can never really know a persons true intent, you must judge them based on their actions and words. Police officers sometimes shoot and kill individuals making threats with toy guns or unloaded firearms. The officer has no way of knowing that the gun was not real or unloaded and neither would any other reasonable person. Therefore, because the officer believed true jeopardy existed, many of these types of shootings do not result in criminal charges.
Preclusion
Your actions will be judged by others after the threat you faced is over. Many self-defense claims fail due to “preclusion” or the avoidance factor. Because human life is held in high regard by society, in many jurisdictions you are required to avoid taking a human life at nearly all cost with the only exception being at the cost of your own life or that of the person you are protecting. After a homicide, law enforcement and others will run through a long list of questions regarding your actions and why you did what you did. If you do not have valid answers and your answers cannot be easily supported by evidence, being prosecuted becomes very likely.
AOJ-P Summary
Never use deadly force against another unless you are in fear of immediate death or great bodily harm, you are innocent, you are a reluctant participant in the altercation, no opportunity to retreat or avoid the use of deadly force exists and your use of deadly force will not put innocent bystanders in jeopardy.