Imagine a software project. Imagine the things that you want to accomplish, the problems you might encounter, the workarounds you could apply, the accidents (both happy and sad) that might happen, the missteps you may take, the steps you can take to prevent them; all of the actions you can perform to manage the project. Now, make a detailed plan that takes all of your expectations into account.
The more detailed your plan, the more likely it will differ from reality in important respects. Unexpected things will happen, some positive, some negative, and many of them out of your control. You can’t predict future events reliably, but you can prepare to respond to them. Therefore: you might want to relax your effort on specific plans somewhat, and emphasize developing skills and resources that will help you to deal capably with surprises.