Metaphor is a figure of speech subtlety comparing two different things. It is also used to represent something more than what it actually is.
The above quotation refers to a coat that should be a perfect fit. I think of this as something or a situation that a person finds himself submerged into. One must be involved in something that complements him perfectly. If a situation is not good for such person, he or she must not force it just to make it "fit".
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Anyhow what exactly did you need
So.. what do you need help with?