In the comments on my last post, STxAR left a comment about his sister and brother-in-law taking on too much tree. They apparently survived the event uninjured. How do you get to be good at something? You can take lessons, read about it, work with someone who already can do it, but in the end it is practicing that brings competence. It might be driving, shooting, martial arts, swimming, algebra, sex, or a million other things. You start out a beginner and you gain experience by making mistakes. Hopefully you survive those mistakes, but it is not always so.
When my son was in college, he took a class on outdoor experience and he shared part of it with me. The instructor spoke about the adventure/chaos continuum and how it changes over time.
I'll use canoeing as an example. You're 12 and at Scout Camp for the second time. You can swim and have signed up for canoeing. The instructor takes you out on the lake every day. You learn the strokes, learn to capsize and right a canoe, learn some basic safety rules.
Years go by. You perfect your strokes, can use a J stroke to travel in a straight line, have done some river trips, learned to read the flow of a stream. You get more adventurous. Other experienced canoeists invite you to take on white water canoeing and you learn more skills. At each stage, it is an adventure.
The thing that changes is your level of competence and experience. As it goes up, the previous experience that was interesting and adventurous is no longer enough, you want something more. What started out as a very safe, supervised activity on a lake is now a kevlar canoe, a helmet, and a high speed descent through a rock garden with no room for error. At each stage, the amount of adventure felt about the same to you. What has actually changed is the margin between adventure and chaos. Yes, your skills are much better, but the situations you put yourself in no longer allow for mistakes. Now if you miss a line between the rocks, you capsize and are swept under into the rocks and pinned.
You can see this in rock climbing, hang gliding, wing suit BASE jumping, and so on. This is not a reason not to do things. It is knowledge to apply to what you are attempting as you assess the risks. Sometimes you just decide to portage around a stretch of rapids.
A tree I might cut on the edge of an open field is also a tree I would hire a bonded professional for if it was near a building. A tree that is solid and healthy is different than one that is rotten most of the way through. I cut one tree for a friend last year in return for the wood. It was 20 feet from a trailer, but I had an open line, it was leaning slightly and the crown was weighted nicely in the direction I wanted to go. I refused to attempt another tree that was also nearby. Told him to hire a pro with a bucket truck.