The reason why you can't execute a task is one of the following:
- You do not have enough time (the time will appear in red).
- You are not in the right context to perform it (you will see, in red, the indicator of the context in which you should perform the task).
- You do not have enough energy (you'll see the power indicator in red).
Take a look to this article for more information: I do not know what to do. I'm lost. What do I do now?