I'll bite.

There is masses involved in the tactics and the different aims of different teams in different stages. Judging when to attack or sprint, or how hard to push yourself on a 40k time trial (too little and you lose, too fast and you run out of energy and lose) is clearly very difficult.

But skill is not the key ingredient, but as other have said being in the peloton cms from numerous other riders at 35 plus mph, or descending at 50 plus mph takes a lot of balls and no little amount of skill.

Cycling is mainly about fitness, endurance, power, teamwork and last but by no means least - balls of steel, and the mental strength to suffer day in day.

And the ability for them to injure themselves but still carry on... From wikipedia -

"[Marteen] Tjallingii was selected to ride the 2012 Tour de France, but crashed on stage 3, he continued for another 40 kilometers and finished it 10:37 minutes behind the winner Peter Sagan. However he did not start stage 4, reportedly with a fractured left hip, becoming the third retirement of the 2012 Tour."