1. The protagonist's family is cruel, insensitive, or ignores them. Alternatively, they are all dead.
2. Friends stab your protagonist in the back...or the front. Metaphorical and physical stabbing from supposed allies is a great way to make your protagonist feel blue.
3. Weight of the world is on the protagonist's shoulders. They must protect their friends, family, and perfect strangers, without any of them being aware of the fact.
4. The protagonist's freedom is restricted and they are left powerless. Oppression to the max! Most effective with women and teenagers.
5. The love interest treats the protagonist like dirt. Depressed and left without a fighting spirit, the protagonist then falls into their lover's embrace. Quintessential love story in the making.
6. Your protagonist thinks that dying doesn't seem like such a bad idea. This thought occurs at least once in the story. Apply as needed.
7. The weather reflects your protagonist's mood. Your protagonist is sad about this, even though there are tons of other people who do not get such preferential treatment.
8. The special gift or ability bestowed on your protagonist is a curse. Why can't they just be an Everyday Joe? Like that insignificant minor character over there...who just exploded.
9. No matter what feats the protagonist overcomes, their emotional state must be on the constant plummet.
10. As long as your protagonist gets hit with every emotional and physical hurdle imaginable, the reader will continue to sympathise with them, regardless of how often they mope and sigh like a prince with the wrong breed of puppy.
Please excuse me while I practice my dramatic exhale.