There you are, popcorn in hand, watching the first great film you've seen in months. The action is racing along, with various bit-part-players meeting unfortunate ends along the way - but your favourite guy is still going. As the story enters the final act, you edge further forward in your seat. Nothing could possibly derail your enjoyment of this film - nothing except... did they just shoot the best character?
It's a sickening feeling familiar to us all (see Serenity/Saving Private Ryan/Atonement for further details) - often because we were too naive to see a character's death coming. Had we taken a step back, considered where the story was going, we might have prevented ourselves from storming out of the cinema in a popcorn-spilling rage.
What we really needed was some kind of acid test - a formula for determining whether our favourite characters is likely to face the chop to prepare us for their inevitable demise. Something like this flowchart from Dorkly.
More a wry-joke than a fool-proof tool, this flow chart will give you a pretty good idea if your favourite character is going to make it to the credits. Best take some tissues just in case?