They are the final say on legal interpretation. Outcomes are for legislators to worry about.
And, I mean, Trump literally said that he could guarantee he was going to appoint justices that would overturn Roe, and then they did, as he guaranteed. That's an outcome, right?
Constitution, Article 3
> The judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish. The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behaviour, and shall, at stated Times, receive for their Services, a Compensation, which shall not be diminished during their Continuance in Office.