Except for our pompous means of comfort, human condition is not much different from animal condition - we are tormented each day with animal like anxieties, insecurities and fears, and each torment makes us believe that perhaps having more comfort will change our condition, but it never does, rather, it only shoves us deeper into the abyss of psychological darkness.
There's sometimes a tugging feeling you get to push further when you aren't being challenged enough or when things get too comfortable.