When I write, I often begin sentences with "and." But when I edit other people's writing, I usually delete those "ands."
When I edit feature articles, I don't change "like" to "such as." But when I edit advertorial articles, I do.
I often point out that sources like "Webster's New World College Dictionary" say it's fine to use the word "healthy" as a synonym for "healthful," meaning "promoting good health." Yet I applaud the Los Angeles Times' habit of frequently opting for the more conservative "healthful" in its weekly Health section.
In fact, there are lots of language precepts that I might follow on a Monday, but disregard entirely on a Tuesday. Does that make me two-faced? Hypocritical? Fickle? Does it mean I have a congenital inability to remember grammar rules? No, it just means that I'm taking into account one of the most important guidelines of all: context.