Well, Basso is doing both. That said, I don't doubt that more racers are looking to optimize their wins. Going balls out at the Giro, resting, and then maybe going for the Vuelta may be a better strategy for Danielson at this stage of his career than doing the TdF.
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“Courage is going from failure to failure without losing enthusiasm." (Churchill)
"I am a courageous cyclist." (SpongeDad)