Take the weather, for example. Photographers can plan their shots and the gear to take but still be at the mercy of the weather. Even following weather forecasts, the weather can still ruin what you plan on photographing. But what separates veteran landscape photographers from novice ones is their ability to adapt to the weather and make the most out of what they have. Sometimes, all you need to do is wait for the clouds to clear to get your perfect shot.
Of course, it goes without saying that by the time photographers get to their destination, they need to know the technical stuff such as camera settings and the like. They need to have scouted out the area and have a basic idea of the vantage points. And they need to be prepared for a bit of hiking, which Robert Testagrossa mentions is quite fun.