I chose physical. If you have to choose between the two, but agree that there is an element of both.
The mental needs to be there to push the envelope on the physical, but the bottom line is that the little engine that could, actually could. If the engine didn't have the capability, it would be sitting at the bottom of the hill wondering why it isn't at the top, even though it knows it can make it.
When you bonk, does mental give you energy to go? Yes, but only to a point. Physical conditioning is needed to accomplish your goals in cycling.
An example, Lance has the mental attitude, but if he had my physical ability we would have never heard of him.
Oh ****, I hate defeating my own arguments, but I just realized that if Lance had his physical abilities, but not his mental aattitude, we would have never heard of him either.
Oh well, I still think the balance leans toward physical, but mental is needed, as it is in everything we do.