The word plan suggests a document, something bound and printed and filed away. The useful part is none of that. A plan is the set of decisions you have already made before life forces them on you.
It matters when the market falls thirty percent and you already know you will not sell. When an offer arrives and you already know what your savings rate can absorb. When a parent needs care and the money for it was set aside years ago, quietly, on purpose.
A good plan is mostly invisible in ordinary times. It does not generate activity or novelty. What it generates is the ability to meet an event with a decision you made calmly rather than one you improvised under pressure.
Which is why plans need maintenance rather than reinvention. Circumstances shift, and the plan should absorb those shifts one adjustment at a time. If yours has to be rebuilt from scratch every January, it was a forecast.