“Chance favors the prepared mind”, I’ve read somewhere as a famous quotation. Planning for all practical possibilities pays off every time. The best example is interview preparation. Once you’ve gone over a long list of possible questions and your answers to them, almost nothing remains as surprise. A nice side-effect is that the effort commits responses to memory in a way that they sound spontaneous, yet have the core value intact. For interview, I suggest even preparing responses to questions that you don’t have a response for; like ” that’s an excellent question, I want to make sure I understand it correctly. Can you phrase it another way?” That gives you time to think of an answer.
Note: If you absolutely have to go unplanned (say for a road trip), plan for being unplanned. E.g. take a GPS, phone charger, etc.