Traveling fast over complex technical terrain requires a high level of technical ability and the endurance to support it. These two quite divergent capabilities need to be developed over years of practice. Omitting either limits your potential.

On big routes in big mountains, speed equals safety.

In the mountains, fatigue is the biggest controllable limitation that will come between you and success.

Historically, many of the great names in alpine climbing seemed to have just gone climbing as training. In fact, the model alpinist has often portrayed himself in literature as a half-crazed nonconformist, living life on the edge every moment he's sober enough to climb. It is true that amazing feats of skill and daring have been accomplished using this rather random approach. For some climbers that "life on the edge" approach may be the only way they can accomplish these feats, but there are far better methods to prepare for the challenges of alpine climbing.

You will never exploit your full technical capacity if your fitness remains a weak link.

I can respect the gulf that separates alpinism from a running race and still appreciate that the physiology that accounts for endurance is the same if you are running a foot race in the city park or front pointing up the second ice field on the north face of the Eiger.

The descent is often as much (or more of) a challenge as the climb.