I've got two points to make in this post, maybe more. First, you can't f*** your plan if you don't have one, so make one. The process is useful because it forces you to look out into the future and consider where you're trying to get to. Once you know that it's easier to figure out what the milestones along the way are going to need to be, and in what order they need to happen. The process can, and should be hard. If you're doing it right you'll find problems in your initial plan. Milestone 3, leads to 4, leads to 5, but it turns out you need milestone 5 to be accomplished to achieve milestone 3. Back to the drawing board. Better to go through this process yourself than have some exec or v.c. do it for you - or the market.
Second, you need to realize that a plan is a snapshot based on available information at the time, which is imperfect. You just can't wait until you have complete information, because it won't happen. A little ways into your plan something is going to change from your initial assumptions; you'll ship late, you'll get a wave of unexpected customer feedback, your product will be unsuccessful, or wildly successful, you'll sign a major deal or one will get terminated, a competitor will throw a curve-ball at you, whatever. Something is going to potentially invalidate your plan. You can do one of two things. You can plow ahead with your plan (because it's a plan, right?), or you can adapt your plan to the current environment. Ultimately, the people that do the former, or are slow to shift to the latter, will be unsuccessful.
It might be a matter of moving some projects around, axing projects completely in favor of new ones, or drawing up a new plan from scratch. You may lose a few points initially when acknowledging your past plan has been invalidated, but you'll gain points in the end because you'll have a better shot at achieving results with a new or revised plan.
Finally, by making a plan and establishing goals, you're creating an extremely valuable learning experience. If you miss your goals, you'll be forced to look back at your plan and its assumptions, and determine where you went wrong. You can then apply this lesson learned to the next cycle. If you never planned, you would never have been off-plan, and you wouldn't have learned anything from it. And if you're not continually learning and getting better at what you do, it is you that is f***ed, rather than your plan. Your call.