Why do we take up our Cross?

Chestnuts and pretzels in NYC w/ bff Pam

What difference does it make to take up our Cross and struggle to overcome our selfishness?  Why even bother?  Imagine if everyone lived just for themselves.  Besides being an incredibly lonely world, it would be an incredibly empty world.  What is it, in life, that fills us?  Why do we spend so much time, energy and anxiety caring about what other people think?