For some electrocardiographic findings the diagnosis is apparent at a glance. It can't be anything else. For other presentations there is a list of causes and diagnosis based on your first hunch may be misleading. This is true of the tall R in V1 (usually seen as R wave amplitude larger than the S wave amplitude) where, if you jump to the more obvious causes such as RVH or posterior infarction and don't make a list you are likely to overlook less commonly appreciated entities such as hypertrophic cardiomyopathy and WPW. The pattern is nicely explained, along with a discussion of the concept of differential diagnosis (listing the causes) at the ECG Interpretation blog.
I cited an article on this topic awhile back and came up with a slightly different list but you get the idea.