Around the eye the anatomy list is long, and a new injector should know every item on it before treating the tear trough.
The structures to know
PubMed Central lists what belongs under this heading: "Periorbital anatomy Orbital septum, tear trough ligament, and its anatomy, orbicularis retaining ligament, arcus marginalis, lateral canthal tendon".
Each name on that list is a structure a clinician in Parsippany, New Jersey should be able to point to on a model before touching a patient. Study with a cadaver where a course offers it, and keep the facial muscles in the picture.
What it costs when it goes wrong
PubMed Central describes the range of outcomes in a paper on periocular filler: "Complications range from mild superficial skin irregularities to granuloma formation to vascular occlusion leading to skin necrosis or even blindness."
That paper is complications after cosmetic periocular filler: prevention and management. Its title names both prevention and management, and a good course teaches both.
Two names before the tear trough
Before treating the tear trough, name the orbital septum and the tear trough ligament, and say what you would do if the result went wrong. If you cannot, the area is not yet yours to treat.