This statement means that it is self-limiting to subject our lives and decisions to patterns that we are already used to.
Explanation:
A hobgoblin is a spirit creature known in folklores as being mischievous. Consistency is depicted to be a negative trait as it is compared to something mischievous.
Ralph Waldo Emerson hereby implies that it is a mischievous or menacing attitude to get ourselves into a pattern because it is what we have always known to be true. This pattern limits us and prevents us from thinking outside the box.
