Russ Cox made a good comment on the golang-dev mailing list about the philosophy of naming variables. He links to his original short post on the subject as well.
A TL;DR version is that
i makes more sense than
index when you're looking at a small loop. For local variables that are only relevant for a short number of lines, having long verbose names actually makes them less efficient.
As the context or reach of a variable increases, having longer names (to a point) makes sense. This can be seen in publicly exported types, methods, functions, constants, variables, and even the package names themselves.
Russ Cox expresses this succinctly:
A name's length should not exceed its information content.
And I agree.