Errant is a peculiar word in the English language: it has two almost opposite meanings. If I am a knight errant, I am a knight going about the manly purpose of saving damsels in distress, and doing honorable deeds. I am onto doing things related to the Spanish ir, to go.
However, if I am an errant human being, I am doing the wrong thing. I have sadly fallen into the situation where I am not helping that damsel at all, I am doing the sort of thing which is not honorable, but related to the Latin errare, to make a mistake or stray.
Believe me, ladies, I want to be the Knight errant, and so far into the past I have succeeded. My model is a white-robed, stalwart man from two thousand years ago, who was born on Christmas Day.