Your ten-year plan will get rewritten about five times. Plan anyway; the planning is the training.

Plans get rewritten because the person who made them keeps learning, which means the rewriting is a sign the process is working rather than evidence the plan was bad. The value was never in accuracy. It was in the thinking the plan forced you to do about what you actually want.

Make the plan anyway, in enough detail to be wrong in interesting ways. Then look at it twice a year and change whatever the last six months disproved. You are training the judgement, and the judgement is what you keep.