Building with stone is not difficult. Assuming the basic rules of masonry are followed, construction is straightforward. However, it invariably happens that at some point, often about halfway into a project, the structure somehow looks, well, all wrong.
It is important to keep in mind that unfinished masonry will look rather dubious. The key is to keep in mind what the finished project will look like, and not be discouraged in the middle of the project.
It is a good rule of thumb never to take down what you have already built, even if it seems wrong somehow. Granted, there may be times where it is advisable to reset or replace a stone, such as if it was accidentally dislodged or broken after having been placed. Beyond that, however, it is best to keep building on what was already placed, keeping the final goal in mind. The final results invariably are far better than would seem possible about halfway through. And, of course, practice makes perfect, and each structure will turn out better than the last.
Stone Arch Bridges 