We get bored. If we don’t get bored, we still don’t like the idea of joy without variety.
For what it’s worth I think this popular sentiment is misplaced. Joy without variety is just as good as joy with variety, but most people either never experience it or fail to realize they are experiencing it and so don’t learn that joy without variety is equally good to joy with variety. Instead I think most people experience rare moments of peak joy and since they don’t understand how they happened they come to believe that joy comes from variety itself rather than anywhere else.
For what it’s worth I think this popular sentiment is misplaced. Joy without variety is just as good as joy with variety, but most people either never experience it or fail to realize they are experiencing it and so don’t learn that joy without variety is equally good to joy with variety. Instead I think most people experience rare moments of peak joy and since they don’t understand how they happened they come to believe that joy comes from variety itself rather than anywhere else.
Perhaps hobbies are areas where people understand this about themselves, albeit narrowly.