It is even larger than an understanding. It is an obligation.
How can real communication occur if both parties - the one offering, presenting, or delivering the message and the one receiving it - don't have a clear understanding of what is being conveyed?
As the person presenting the message, we can code or hide what we say in such a way that the person whom we are addressing hears what they think was being said but really does not know, and therefore can't work with, what we truly are saying.
If we use words, idioms, or phrases that can have multiple meanings or ones that are inconsistent with the vocabulary or language skills of the person we are addressing, they can't possibly understand or know what we are saying. Communication has not taken place - only delivery of a message by us and the hearing of it - but not comprehension - by the receiver. We might as well be speaking to them in Latin or another language that they didn't speak or understand. The meaning would still be unclear to them.
The purpose of communication should not be for us to feel good about what we say or to hear the wisdom of our words. It must be to reach the other person on their wavelength, in terms they understand.
Communication does not occur when one delivers a monolog or soliloquy. There has to be a minimum of three parts to any communication - delivery of the message (even if it is written or nonverbal), receiving of the message by the person meant to receive it as the only one to whom the message was directed or as one of many people being addressed, and a comment or acknowledgement from the person hearing or reading the message that they understood what was being conveyed. Otherwise, it's just so many words being offered by the speaker or author of the message.
Refusing to take responsibility for what one is saying or writing - and leaving the interpretation and understanding of it to the person hearing or receiving it - is a very irresponsible approach to delivering a message.
Making sure the person seeing or hearing our message has gotten a little more complicated in recent times with the coming of the text message and email. There are so many ways a particular word, phrase, or combination of words can be misinterpreted based on someone's mood when they read it or their life experiences. Something that we say quite innocently or with the best of intentions can seem hurtful, rude, or inappropriate when someone reads it that way.
We all apply filters to what we see and read based on past experiences and distractions - other things that might be occupying our minds or competing for our attention at the same time. We don't and can't always know this, but we can take it into account by choosing our message very carefully. If there is the possibility that something could be misunderstood - because we see how that could happen - we need to rephrase what we are saying or not send the message at all.