As I see it the possible outcomes of having a life plan are these.
1. You achieve your planned objectives, and you’re disappointed by how it feels.
2. You fail to achieve your planned objectives, and you’re disappointed by how it feels.
3. You achieve your planned objectives, and you’re happy with how it feels.
So you’ve got a 1 in 3 chance of success! But who knows, even if you achieve number 3 and you think you’re finally happy, you might have missed loads of other, better, different stuff whilst you’re narrow-mindedly pursuing your plan, which was probably flawed in the first place.