According to Osho, doing nothing is hard because it offers no challenge to the ego, which survives on effort and difficulty. Idleness starves the ego, and sustained non-doing leads to its dissolution. Meditation is precisely this art of 'just being' (initially tough but increasingly effortless once you taste its simplicity and deep relaxation), revealing action itself as the real problem.
Doing nothing is tough because your ego wants to stay busy to feel important, but with practice it relaxes and lets you just be.