Left to ourselves, human beings cannot sustain anything merely for the joy of it.
We need a purpose, an end Goal for us to sustain things. Be it the maintenance of relationships, training or pursuit of knowledge, without a purpose, we fall apart.
A purpose makes discipline a necessary yet easy to do thing.
So getting down to practical application to this theory, for example, if one has a circle of friends that one really cares for, thence its best whence there is a greater purpose ,other than joy and camradiership to get together, like maybe music or worship or any kind of hobby or just a clearly articulated purpose. Else time and new things will erode these relationships away.