She is sunshine on a cloudy day. When it's cold outside, she is the month of May. (from My Girl)
I wandered lonely as a cloud. (Wordsworth)
black as night
sharp as a tack
guilty as sin
These are not obscure. They may be oblique however, choosing a different path to get to a truth. Sometimes comparative metaphors end up being clichés due to overuse. Metaphor creation, therefore, can be a bit tricky.
A controlling metaphor is one that dominates (controls) an entire literary piece or is ubiquitous in a person's speech. For example, a character or a live person may refer to things in light of certain images or actions. Constant references to food for example may indicate the person sees life as a banquet. Depending on the tone of the piece or the tone of speech that may further indicate that the person sees life as a banquet to which she/he is not invited. The use of controlling metaphor is a great way for a writer to enhance a scene or develop a character.
Controlling metaphor is similar to extended metaphor, which extends over a large portion, but not all, of a literary piece. When you read the article linked below, be very careful not to confuse controlling metaphor with metaphor used to control. There is a difference.
Your assignment: READ the article