“In cycling, being sure of yourself is an almost inevitable guarantee of not winning.”
Eddy Merckx was a “worrier”. There was always something in his mind. He was always minding about every detail, and never underestimated his rivals.
There are two sequences in the film “A Sunday in Hell“, directed by Jørgen Leth, which illustrate Merckx’s obsession with position on the bike. Early in the film, which centers of the 1976 Paris-Roubaix, Merckx is shown on the eve of the race in the team’s hotel spending several minutes checking and double-checking the position of his saddle and brake levers.
Fastidiously, he employs a spirit level, long metal ruler, and tape measure. The following morning, when the race is stopped close to the start by a demonstration, his first instinct is to head for a rival team car and borrow a spanner so he can tinker with his saddle again. 
- Merckx: Half Man, Half Bike; Fotheringham, W.; Yellow Jersey Press; London – 2012 (page 138)
- In 1969 Merckx crashed in a derny race in the Blois velodrome towards the end of the season. A pacer and a cyclist fell in front of Merckx’s pacer, Fernand Wambst. Wambst died instantly, and Merckx was knocked unconscious. He cracked a vertebra and twisted his pelvis. He said his riding was never the same after the injuries. He frequently adjusted his saddle while riding – including coming down the col de la Faucille on the way to Divonne-les-Bains – and was often in pain, especially while climbing.
- Eddy Merckx on Wikipedia