What can go wrong..

with your adventure ? Here my top misses: Depending on the activity, damage and loss of equipment can be high. Consider backup gear, spares, tools for repair.

Minor injuries are common in outdoor activities. Many don't need treatment, but you have a medical kit, anyhow.
Serious injuries can be problematic. If there's a substantial risk that a person has to be rescued, think of how to do it before you go. How many people will be required to carry one injured person, given the terrain, the distance, the strength of those who have to carry ? What does it mean when you go alone ? If you go with a partner, are you going to leave an injured person alone for several hours or days in order to find help ?
Though an insurance may cover helicopter-rescue, there may not be a helicopter, you may not be able to call one or you may not be able to convince one to come to the spot where you are. Better live in harmony with your guardian angel !

Here a few stupid and highly dangerous travel scenarios that happened to me or others:

Language problems mixed with US$ are a dangerous brew:
In 3rd world countries, poor guides / drivers / sailors are willing to take unreasonable risks if a customer is ready to pay enough. The customer may not be aware that he's offering 10 times the amount that is normally paid while he will also not understand the concerns explained in a foreign language. He may sink with a small boat in a storm or get fried by lava.

I was talking to a guide in Blankejeren, northern Sumatera. He guided tourists around the jungle. The biggest thing for visitors to happen is that they see a Sumatera Tiger. It's exactly what this guide does not want to happen, but once it happened. While the boy was alone near the Tobacco Huts, a tiger approached him. He froze from fear. The tiger went around him twice, then disappeared into the forest and the boy survived to tell (while others didn't). I asked him why visitors wanted to wander into the forest at all, if that was so dangerous. He explained that they didn't understand how real the danger was. Everyone believed that Sumatera Tigers would be rare, shy and not into eating humans. With each tour earning quite a bit of money, he is doing this job in spite of the risk.

Language problems plus your status can be deadly as well:
Villagers and many children have high respect for a foreigner whom they consider all-knowing and strong. But you are not all-knowing.
You could be poisened by gases that rise at certain times or under certain conditions, something that they explained to you but you failed to understand. As you went on, they believed you had understood and knew such situations, being prepared to handle them.

Inexperienced guides may wrongly judge your abilities:
Local children may know an area very well and be proud to guide you around, but they could expect your skills and physical condition to match theirs. They won't plan for extra time (extra food, extra water, extra batteries) that you may need as you go slow.

So we entered a cave, emerged at the back, climbed the roof of the cave and onto an overhanging rock. Great view from up there. A tall palm tree came up from below, passing the rock at a distance of 1.5 meters. My children-guides proceeded by jumping from the rock over to the palm tree, then slid down to the ground. They couldn't understand my fear but eventually, some of them went back with me on the way we came. Luckily, this was possible.