A life well-planned is boring. You are discipline enough to do the same routine every single day to achieve that "accomplishment" down the long run. You don't deviate from your path, you actually stay true to it regardless of what people say.
Some say, though, that the single-mindedness is required to be successful.
A life not planned at all is a disaster, however. You don't know what do you want to do and will be lost, distracted with too many things for too long, not knowing where you'll end up eventually.
But that also means you're flexible or open-minded enough to jump into any kinds of opportunities that come your way, and it is exciting as there is something new to discover every day when you don't walk on the well-trodden path.
Well, even if you're an advocate of "If you fail to plan, you plan to fail." you could still live an unplanned life lifestyle, or vice versa.
But it really isn't as simple as it seems.