two as one

to stick
to follow
to lead
to flow

can the elbow strike the forearm?

no, because though distinct the elbow and the forearm are one
and though it cannot strike
what control the elbow has over the forearm!

the elbow is the root
to the trunk of the forearm

if you become the root of another
though distinct you will be one
follow and lead

Taijiquan is like this

if the forearm is severed from the elbow
the two disconnected
this is a disadvantage

if you are separated
from the opposing force
you are like an elbow
without a forearm

separation
unity
these things are not to be taken lightly