Impediments to effective interpersonal discussion/communication

Impediments to effective interpersonal discussion/communication. Not mutually exclusive.

1. Lack of trust - the perception of bad motives by your discussion partner.
2. Fear of being wrong - an ego commitment to a particular position that prevents the open consideration of alternatives. 
3. Lack of clarity - a disjoint in the understanding of terms and concepts - sometimes the result of asymmetric prior education and conditioning.

Number 1 is devastating. 2. is formidable. 3. can be overcome with patience and determination.