It doesn't. What it needs to do is work alongside it. The same metal color is the most seamless starting point, but contrast can be intentional. Bring your engagement ring when you come in. Seeing both on the hand is the only reliable test.

Some women choose a wedding band that works independently, wearing the engagement ring only sometimes. An eternity or pavé band reads complete on its own. A plain band carries its own quiet authority. Neither approach needs justification.