A motion to vacate (or set aside) a judgment asks the court to undo a judgment that's already been entered. Courts don't grant these lightly — final judgments are meant to be final, so the motion has to fit a recognized legal basis.
Common grounds courts actually accept
Excusable neglect, newly discovered evidence that couldn't have been found earlier, fraud by the other party, or a judgment that's void for lack of jurisdiction are the typical bases — vague dissatisfaction with the result isn't one of them.
Timing is often the biggest obstacle
Most jurisdictions impose strict deadlines — sometimes as short as 30 days for some grounds, longer for others like fraud. Filing outside the window can bar the motion entirely regardless of its merits.
Show why you didn't act sooner
For excusable neglect claims especially, the motion needs to explain specifically why the default or missed deadline happened and why it should be considered excusable — not just that it happened.
Pair it with a meritorious defense
Courts are far more willing to vacate a judgment when the moving party can also show they have a genuine defense on the merits — vacating a judgment just to relitigate a case with no real defense rarely succeeds.