You don't start because every day you wait makes the task bigger in your head, not on paper. The deadline raises the cost of not starting, but it doesn't shrink the first step, and the first step is where starting gets decided. What shrinks it is one action that takes ten minutes.
Read the full article: https://impruvement.com/blog/why-dont-i-start-even-though-the-deadline-is-getting-closer