Been hurt, but never injured.
Took a ride down a white pine when I was still fresh in this business, no one ever told me they got brittle when it was 10 below, tied into the top, leaned back to set the knot, and took the top with me to the ground...landed in about 3 foot of snow..no damage, except to the tree.
Took a spike through the heel, right through both sides of some brand new boots back in 86, was real upset about the boots. Then realized that my foot was what the spike was caught on. I finished the tree, iced it down, and was back to work the next day...(still cussin about the boots)
Had a real smart-ss boss as a groundman one time, kept insisting I take pieces bigger on an elm removal. Took a piece too long, and the ground men weren't able to control it, pinned my arm against the tree, had to lower the piece over my arm....(nice rope burn...not serious) That was the last time I ever worked for another tree service. As the boss was picking himself up from the ground, (he had a little run in with an angry climber when I got down) I was walking away.
After 27+ years I have never lost a day to an injury doing tree work...I still NEVER work alone. IT is the stupidest move you can make. Your friend is right. No matter how good you are, there is always the unexpected, unseen, and the accident you did not expect. I have never been hurt in a "hard" tree. Always the easy money ones.