I remember a conversation between a senior and a junior colleague of mine a few years ago. The senior had asked the junior to do some task. When it hadn't been done, the junior was asked, why he hadn't done what he was told to do. The response, "I was too tied up; there was hardly any time to do that."
The senior's retort was: "Did you have time to brush teeth? Did you have time for a meal? So, don't tell me, you didn't have time. I won't believe that. Tell me, I didn't want to do it. I will believe that."
A bitter truth, is it not? "I didn't have time, is the most common euphemism to say it wasn't important for me.
It all boils down to priorities. We all have more stuff to do than is humanly possible to do, with 24 hours in a day. We need to prioritize.
So, why we do what we do? Because it is important.
What is less important, can wait; they give way to what is more important.