The ability and desire to really Listen.

Poor listening skills seems to be an obstacle. 

Not answering the phone/text/email? How can you talk if you can not reach a person? 

Not listening!

Not listening.  A

Timely responses. If late in responding, the other party is usually deaf.

Good communication requires good listening and then comprehension.  If you don't have all three you are missing the mark.

Listening is a problem.  Another is you think you say one thing.  They hear something else.

Therein lies the difference between hearing and listening, the latter is becoming a lost art.

Non responsive parties can make life difficult.

People who either talk non-stop and refuse to listen, and then once you force them to listen, the only thing they're listening for is their next opportunity to talk.

Probably the biggest obstacle is people not really listening.  

Instead of being the talker listen, really listen to the other person.

Preconceived notions.

Good communication is hindered by getting

Those who do not listen are the most significant obstacle to productive communication.

Talking and not listening.

Annette - I was always taught that communication is a two way street. So if one is always talking and not listening, that is a big obstacle to communication.

Non-repsonsive people!  They drive us nuts.

Listening gets my vote.  But as I was thinking, a lot of communications are destroyed by EGOs

Forgetting we have two ears and one mouth for a reason.  

Most have real trouble listening.  REALLY listening!

Good morning Annette. At times I am right out straight, calling everyone back in a reasonable time period can be a challenge.

Most folks do not know how to listen deeply. They want to talk and wait for the opportunity to say their piece

Our inability to listen.

Not listening so you don't know how to respond.

Reading between the lines what's not being said.  

Judging by how I missed a meeting today by an hour due to timezone issues, I'd say geography.

You only learn if you listen. Everything you say, you already know.

I'll add another vote to poor listening skills.

Not being open to other opinions.

Annette,
As someone who has done some pastoral counseling through the years my vote is honesty, or the lack thereof. If people aren’t honest with themselves and others real communication is very hard.

Myself

What is said and what is heard are often worlds apart. That may be the illusion that communication has taken place.

procrastination.

I think the biggest obstacle is understanding what the other is saying. We hear and put things in our context which might not be what was meant and vice versa. so confirmation that was was heard was what was meant

Vibes go a long way.