I replaced all 4 springs at my old house. One had both sides fail at the same time...getting the door open required 2 people, several hydraulic jacks, a set of jackstands, a bunch of 2x4s, and about an hour or swearing.
There's a seasoned carpenter near me who needed help installing a garage door about two months ago. He's getting up there in years and didn't feel too comfortable installing the two springs himself, so he had me help him. (Although...perhaps I'm not a spring chicken anymore, either )
This job was an a garage that had been extended and the garage door and all pieces were a new install. This particular door had to be wound up to 16 markings of paint. I will admit that your nerves are stretched to the limit while doing it, at least mine were. The carpenter had all the tools, I supplied the muscle. While we were on a roll, we went to his son's house and did another one.
This is one occupation that I wouldn't do for a living.