When I’m enjoying something, there is also a hidden element of unhappiness attached to it. This is because I’m afraid that the thing, which I am enjoying, might disappear any moment. If I have common sense, I must know that I can’t enjoy the whole thing all the time. So, the moment I enjoy something, there is already a hidden agenda of holding on to it, because it might slip away. This itself is unhappiness, you see. So, in happiness, there is a small element of unhappiness involved.