A plan is not a prediction. It is the order you do things in: debt, then a cushion, then investing, with a mix you chose before any market moved.
Written down, a plan survives a bad week. Kept only in your head, it bends to whatever the market just did, which is exactly when it is most likely to be wrong.
A plan is a handful of settled numbers: your cushion size (often 3 to 6 months of spending), your mix (say 70% shares, 30% bonds), and how far a fall can go before you act.
Changing the plan after a scary headline is not updating it, it is abandoning it. A plan is tested exactly when you most want to break it.
Portfolio's My plan panel keeps your mix and limits in one place; a line in your journal keeps the reasons next to the numbers.
A plan is the order you chose before a market moved. Writing it down is what makes it hold.
Write it in Portfolio or your journal.