This happened in the late 70s, when I was living in a cabin under the butternut tree at the family farm in Quebec. I was out of college, between jobs and helping my friend Barry build his great big house (castle, really) up the hill and in the woods. 
He had dug the foundation and poured the concrete the year before, and when I joined him, he was ready to start raising walls and roofs. The place was built of 12 by 12s, square logs piled and joined, forming the thick walls that would insulate the house. The ground floor was one big room with a kitchen at one end and a fireplace at the other. There was an open staircase leading up to a big bathroom and two bedrooms. It was a big, solid house, but really simple. The fanciest thing in it was the antique copper bathtub.
At the far end of what was to be the master bedroom was a ladder, which led up to a small third floor tower room with one big window, This tower room, with its view of the lake in the valley and the mountains beyond, was the best thing about a fine big house, and while we were building it, I lived up there.
This was in the fall, and nights were chilly. The room wasn’t closed in yet (the house was still half built) and there was no window. I had two arctic sleeping bags, a bedside light and a radio, and all the great outdoors to lull me to sleep. I occasionally entertained up there, with my grandfather’s bighorn ram’s head looking down from the wall above the bed.
One night, later in the fall, when it was crisp, I got in my brother’s car to drive down the hill for a case of beer from the dépanneur at the bottom. He was at college in the US and had left his car behind. It was a worn out 1967 Volvo 123 GT called Greta. This was the period when Volvos looked like 1950s Soviet taxis, round and workmanlike. 
The 123 GT was special though. For one thing, it was a two door (unimaginably sporty for Volvo) and it had the GT package, with the same 2.0 litre engine the Volvo sports car had. I could get Greta up to 110 miles an hour coming down the hill from Stagecoach Road. Not legally, mind you, I had neither a license nor insurance. Quebec was a bit wild and lawless then, insurance wasn’t required, and no one ever asked to see my non-existent license.
By the time I had Greta, she was missing a front fender and the battery was gone. To get around, it was necessary to always park on a hill (it was a hilly county) so you could coast to a start. Many times, I’d had to leave her at the side of the road and walk home when I unthinkingly stalled her on the flat. 
That night, I had parked it, nose up the hill beside Barry’s new house. I got in, put one foot on the brake and one on the clutch, turned the key, put it in reverse and opened the driver’s door with my left hand so I could look behind me as I jump-started it in reverse. This was a maneuver I had completed many times before, but this time was different.
I let the brake go, felt the car pick up speed and prepared to let the clutch go and bump the engine into life. I was holding the door open with my arm out and didn’t see the young but stout tree the car was backing on to. Greta rumbled down the hill, the engine coughed and the tree crashed into the open driver’s door, with my arm sandwiched between. The car groaned, the door creaked and bent backward on its hinges and everything settled into place, with all the weight of the car on my arm.
It hurt like hell and was bent at an uncomfortable angle. The first thing I did was put a foot on the ground, my shoulder to the doorframe and then pushed with all my strength. The car didn’t move. It weighed a ton and a half and I weighed 140 pounds. I was the strongest and most fit I’d ever been, from carrying logs and hammering nails into beams, but I couldn’t lift a car like Superman.
The next course of action. Call for help. Barry’s new house was a quarter of a mile up the hill from the farm, no one between. Nonetheless, I yelled for about 10 minutes until my voice was gone. Try everything once.
Another try pushing the car up the hill off my arm. It led to some creaking and groaning but no movement. Part of the problem was the inside of my arm was pressed against the door panel with my elbow sticking out. This limited movement and didn’t allow for very good purchase when pushing.
OK, next. Wait for help to come? I wasn’t expected anywhere, I was living at the new house, no one thought I’d be anywhere else. Barry would come for work in the morning, a day hence.
Next. This sounds overly dramatic, but it was very late at night, it had been more than an hour, I was getting cold, my arm was numb and I was panicking. I had a Swiss Army knife in my pocket. You’ve heard of the film 127 Hours? Well, there I was, wondering if I could cut off my own arm, and seriously considering it, 40 years before the film was made.
The thought of trying to perform auto-amputation (I have a very vivid imagination) did it. I got up once more, curled into my trapped arm as tightly as I could across my chest so my back was against the door frame, dug my heels in the gravel and just barely forced Greta far enough off my arm to snatch it out from between the door panel and the tree. As I let go, the car slid back down on to the tree, groaned, cracked and the door bent back 45 degrees. That was how much weight was on my arm.
I stayed at the farm that night, my arm wrapped in ice. It got better, but whenever I butt up against the impossible, I think of that Swiss Army knife, and give it one more shove.