Photographers in general are at the mercy of moments and time. Nature photographers are more so than any other photographer. It takes a lot of preparation and planning to make a good image. Even when all that planning comes together it's often changed by other factors. Don't force it! Let the things you can't control, just happen. "Sometimes delaying action can be the best action". Nature photography is often dictated by nature. If you make plans for sun, it will probably rain. When I travel, I make a list of images I want to make, and what weather conditions would be best for those images. Once I arrive, I let nature dictate where and when to photograph said locations. Making a strict schedule, or even a strict shot list, would eventually cause missed photographic opportunities. It could be as simples as the better light is behind you and not in front of your lens.
Always be aware with what is happening around you. Instead of photographing the setting sun, look around and see what the sun is doing to the clouds or landscape. Don't force an image. I have found myself at a certain local when the conditions changed for the worse. The conditions would actually work better at such and such place. I then drop everything and head to the other location.
Like an architect working with a builder, what looks good on paper may not be practical in the field. The architect will often have to revise his blueprint to a better all around solution. Forcing the issue could produce an undesirable result. We as photographers are the architect.