These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Deltora Quest
Anvilicious - GAMBLING AND DISHONEST MONEYLENDING ARE VERY VERY BAD, we get it already, please put down the hammer Miz Rodda ma'am....
Clarke's Third Law - A fair amount of what the Shadow Lord does sounds more like our technology than magic. From the lights in the Gray Guard growth building, to the "sparking rods", to the reference to the power being cut, it's easy to conclude that he's using electricity, which the heroes have no way to distinguish from magic. Whether the generation of Gray Guards is magic, science, or a bit of each is hard to say.
Harsher in Hindsight: After the gang is captured by the people of Plume in series 2, Jasmine sarcastically asks Glock if his talisman part of which is actually the Pirran pipe will protect him from The Fear. The Fear ends up crushing him to death (on the bright side, he deals the killing blow to the Fear single-handedly, and the Plumes and Jasmine come to honor him as a hero for his sacrifice).
In-universe, the opal out of all the gems. Lief hates touching it, since it usually means impending Nightmare Fuel.
Replacement Scrappy: In-universe; Paff replacing Ranesh as Josef's assistant in the library. Her apparent ineptitude helps her real goals go largely unnoticed until almost too late.
The Woobie - Oh hey, Jasmine! Let's talk about your life. You grew up in a forest. When you were seven years old, your parents were taken away, presumably to be killed, and your home got burned down. You had to fend for yourself. When you were sixteen, two strangers invade the lifestyle that you made for yourself, and your dead mother's spirit made you leave your home to go on a quest with them. You had lots of trouble because you could barely read or write, and most people thought that you were mad. Then it turned out that the guy you kind of liked was a servant of the Shadowlord, and not even human! Eventually you discovered that your father is not really dead but all that he has been through has made him a completely different person. And then it turns out that the other guy you kind of liked was the heir to the throne and became King. Later, you found out that you had a sister, Faith, in the Shadowlands. Another guy you kind of like dies on the way to the Shadowlands. Oh, and Faith? It turned out that she was not real, but a plot of the Shadowlord's to get the King into his realm. And the Shadow Lord says explicitly that you were never important in his eyes, just a pawn that could be used against Lief.