Do we struggle to relax and rest?

During my yoga session the other morning, the instructor encouraged us at the end of shavasana to remain in the pose if we had more time and not to be afraid to rest. Immediately, I found that statement peculiar. Why would rest provoke fear? The answer became apparent as soon as I posed the question: many of us struggle with the idea of rest. Considering our perpetual busyness and lack of time, it doesn't seem far-fetched. Consequently, rest can appear as a threat to our accustomed way of life, rendering it exceedingly challenging to quiet our minds and truly unwind. Why do we do this to ourselves and what can we do to fully rest?