What should you do when your planning fails?
First and foremost: Don't give up on planning! Don't fall in the trap of saying that planning is just simply not for you.
We all need a planning - the degree of detail of planning might differ from person to person, but the question of what we should be doing and when to get stuff done, is essential to all of us.
Until you have found a planning method that works, I encourage you to do the following: test out different methods, try out different tools, and reflect on what works for you and what doesn't.
This method might sound like throwing spaghetti to the wall and seeing what sticks, but if you evaluate how you do with planning honestly, and try to figure out why a certain method is not working, then you'll reach convergence and a working system much more quickly.
Here's a quick recap of a Twitter discussion I had on this topic:
For your convenience, here is the link to the Monthly Progress Monitor, and the programmer method of scheduling time.