Hiking is dangerous. All everyday activities may have their dangers, but hiking isn't for everyone. Trails aren't always maintained and that guy you see climbing up the side of the waterfall without equipment might have the training and experience to do it safely.
If you see a sign warning you not to cross, don't cross. If a ranger tells you the trail is unsafe, take a different route.
Matt and I research our hikes before we start. We bring the ten essentials on every hike. We never hike alone and we pay attention to warnings. We watch the clouds, we listen to our bodies, and we check the time often. We slow down or turn back when necessary. We know what to do in emergencies and how to avoid them.
In spite of all of this preparation, we've still been in dangerous situations. At times the fault is completely ours and we could have been better prepared or made better decisions, and other times we've just encountered unpredictable dangers and been lucky to avoid injury.
The hikes I do are not for everyone. They are all dangerous if you're unprepared or inexperienced. Please be fucking careful.