co-: together, with
sist: derived from Latin "sistere", meaning "stand"
So coexist means:
Stand(go) out together.
Standing(going) out to look for food means "to live, especially under difficult conditions or with very little food or money". So coexist means "live together, or exist together".
Evolution of usage
We need learn to stand(go) out together with different people.
We need learn to exist together with different people.
We need learn to coexist with different people.