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As someone who just created the general outline of a five-year plan (my first one), I'm wondering what other HNers have to say about the subject.
That is, you need to do the planning to look around and see e.g. what your strengths/weaknesses/opportunities/threats are, what your objectives are, and what direction to set out in. Otherwise you run the risk of paralysis or being permanently behind events.
On the other hand, reality deviates from the plan immediately, for better or for worse. But at least you have the information gathered from the planning phase to re-plan from.
When I look back to 2011 I'd never have guessed that I would be where I am, doing what I do, today. I'm confident I'll be able to say the same in 2021.
My parents grew up with the "one-company-for-life" mentality, but I'm a firm believer that it's good to mix things up every few years to keep yourself fresh and motivated. That's not to say you should abandon something that you're truly passionate about if you continue to derive long-term enjoyment from it, but rather be open and flexible to new opportunities as they may take you places you'd never imagine.
A general outline is useful to have. A useful four-year plan is kind of like "graduate from college". Lots of room for improvisation along the way, but the ability to measure if life is headed in the direction you want to be headed.
In practice, I've found it impossible to follow a plan beyond two years due to external factors (friends and co-workers move, industries change, laws change, deaths, etc.). Those external factors seem to speed up with age. However, having a "general outline" (like waypoints on a journey) helps to correct course or select an alternate path when those inevitable changes happen.
A plan isn't a bad thing but being overly committed to it can be fatal. One of the things about publishing a five year plan for a company is that you are usually judged in the markets by how closely you stuck to and succeeded in that plan. In tech, and probably most other industries as well, that can be fatal. Publishing a goal is a little less fatal since it doesn't outline a series of steps toward reaching that goal and allows you flexibility to pivot. Assuming of course that you didn't phrase your goal in the form of a plan or get too specific or detailed.
That similar trend has shown up in my personal life too, although not as often.