Why do small tasks feel impossible when you are already overwhelmed?

Because the difficulty is not in the task, it is in the decision-making capacity that is already depleted. When cognitive load is high, initiating anything requires disproportionate effort, and each pending item consumes attention even while untouched. What helps is reducing decisions rather than increasing effort: write everything down so it stops being held in memory, pick the next action rather than the most important one, and shrink the first step until it requires no planning. Doing one thing usually restores enough capacity to do the second, which is why starting anywhere beats choosing well.