This is not meant in a manipulative sense - it means people want to impart their deep understanding of some things but are forced into the construct of short conversation and language.
Though you want to try to deliver your knowledge/feelings/understanding to another person, rarely can you conjure a perfect few sentences to encapsulate all that you mean. And if those words did exist, it can hardly come up during everyday conversation - you simply don't have enough time to put thought into your words, you just have to spit out whatever is closest in your mind.
Take this into mind during your conversations. Realize your conversation partner's frustration with complicated subjects. Try and extrapolate their thinking, and don't be passive. It's very discouraging to have to do all the work in a conversation without helpful probing questions.
This becomes especially important if something is said that pushes barriers or buttons - try and understand how that statement makes sense instead of recoiling defensively. (Though take this statement only with your closer relationships, as people saying offensive things early in relationships have their own complications)