I cannot quite remember my first 200K or double century but I do have a relevant memory. Us youngsters thought we were hot **** riding really hard charging hills and we would be sitting eating and resting while this seemingly slow turtle of a rider on a Spectrum titanium would mosey by. We'd do fast 200k but would be destroyed to do 400k. After 300K, we would never see this fellow again. He was a steady Eddie. Funny because his name was Ed and was one of the head guys at a famous bike magazine. Not saying he was slow, more like very smart.
Learning the correct pace can be hard to do. There is always that old saw....don't burn matches. When I learned to ride within myself and let faster climbers go, it got easier but randonneuring is not for the meek or weak.