Customary usage establishes a familiar connection; a contextual clue helps identify which meaning is intended here and now. The two perform different tasks. One explains why an expression is associated with a meaning, while the other directs us toward the meaning the speaker intends in a particular utterance.
If a poet calls a brave fighter a “lion,” the customary association with courage supplies the route of understanding, and the human setting excludes an actual animal. In an account of a wildlife exhibit, the ordinary animal may instead be intended.
Careful analysis therefore separates recognized association, the listener's knowledge, and the context of the utterance. This prevents mistaking a possible connection for the speaker's actual intended message.