Exceptions to the Rule...identifying trees

In a recent attempt to learn more about trees I've found myself wading through the many ways they can be identified or distinguished from one another. One can look at the leaf scars, the leaves, the leaf buds, the bark, the tree shape, flowers, fruit, among others. In nearly all cases I find slight variations that make an accurate ID a challenge. some trees are young, some old, and some grow differently in different environments. If one were to spend time laying out the variety that exists in leaf shapes and proportions in a single tree, the complexity becomes apparent...especially if one attempts to compare the leaves of different species that are quite similar in appearance, like southern red oak, pin oak, northern red oak, and scarlet oak.
In this fog of confusion, one method works best for me. I use two or more attributes, always. In the following example I use the Sourwood tree (Oxydendrum arboreum), not for variety in leaves, but for variety in the bark. With the sourwood, I've been relying upon three attributes for confident wintertime ID: wispy seed strands (panicles) atop the trees, the distinctly patterned bark, and the unusual structure of the tree itself. In the photograph you'll notice that great variation can occur with a variation in size. The bark on your left is on a tree with a 4 inch diameter. The tree on the right had a diameter of 8 inches, and has bark that is much more coarse. Were it not for the distinct structure of the tree and the presence of panicles in the tree tops, an ID would have been difficult.
So, the take-away here is that one should never rely upon a single attribute for making an ID. The same can be said for using guide books as sources. Cross-referencing is essential when trying to understand the differences between tree species.
By the way, may favorite (and recently chosen) combination is Sibley (the newly released tree book) and Watts (Winter tree finder). The combo has given me renewed interest and confidence.
Happy tree watching!