Humans get bored at times with even the best activities in the world. It's simply human nature to want more: more challenges, more experiences, something new to add more to our life. In sex, we are told to try new things in the bedrooms. Seniors are counselled to do more activities to keep their brains fresh. Children do well when they are exposed to a variety of activities and so on.
But then again, when things get too different, we get skittish. Another evolutionary bump; too much change signifies something bad is looming and we duck and cover!