He talks about how he got good at standup after 15 years of doing the same thing. He threw away all his material (material he'd been working on for 15 years) and just started trying different things. Then he started throwing away his material every year and creating new material. He noticed that he got better and better by doing this.
This also reminded me of another anecdote I'd heard somewhere where you have a pottery class with 20 students.
The class was split: 10 students would make a new sculpture every day while the other 10 would have to produce only 1 sculpture for the class (which of course would represent all the extra planning and execution that went into the solo sculpture). At the end of the quarter, the 10 people who made something new every day and then threw it away were far better at sculpting, while everyone in the other group made something kind of shitty and spent a lot of time doing it.
So maybe it's not "lack of planning" quite so much as willingness to kill your darlings, again and again.