A - The task requirements and goals might not be clear enough. If you are trying to get yourself to “plan for a project” or “write a book” then it’s hard to identify the next actionable items. Put some time aside to figure out what physical things you can do to move the project forward. Try break down the larger tasks into the smallest pieces possible. The goal of the project might need identifying, or the requirements fleshed out from a supervisor.

B - The task might exceed your current competency. Sometimes we know what we have to do, but don’t know how to do it, and then we become avoidant rather than admitting this. In this case, it’s worth figuring out what you do know how to do and what you don’t know how to do, and be honest with that. Then slowly ask for help or read up on the things you don’t know.

C - The tasks might really not be worth it. Sometimes you are assigned tasks that don’t actually help you achieve your long-term goals, and so your brain demotivate you from doing them. Maybe the payoff is low, maybe you don’t learn anything new from them, or maybe a colleague you don’t like will gain credit for the tasks, or maybe you just wont be rewarded or appreciated for getting the tasks done.

Kind of controversial take on note taking systems. I can relate though, because i was lost in a burden of creating perfect knowledge management system for a long time without creating any knowledge. Simplest approach with commonplace notebook is what working for me now.
Comments are also useful.

Getting lost in your knowledge management system is a fantastic way to avoid creating things.
Most heart-stopping writing comes from synthesizing the previously unarticulated in the moment. Rather than reaching for your database, try channeling what’s in the air at this very second. These read/write errors are what we call originality.
Leonardo da Vinci kept all of his notes in one big book. If he liked something he put it down. This is known as a commonplace book, and it is about how detailed your note-taking system should be unless you plan on thinking more elaborately than Leonardo da Vinci.
Shun the useless adoption of the aesthetic of the useful. When something can be like work or like play, never make it work.

Personal goals are generally expected to happen later.
The reason it’s hard to get going on personal goals is that you’re already using all of your time. No matter who you are, you’re already using all 24 hours, every day, for something. Because this will always be true, goals that happen at all must happen now, while you still don’t yet have time.
Basically, you learn to work in small, uniform parcels of time. They’re short, timer-bound, and unwaveringly focused on a particular outcome. Most importantly, they can fit into real life, as it already is.