Some people find it difficult to express their thoughts verbally. They may often feel that their words don't give their thoughts enough justice, and that their thoughts could've been verbalized better.
This is my opinion. I have no sources for this.
The common concept of thought in Western culture, going back to philosophers of the Enlightenment such as Leibniz, Locke, Hume and Descartes in the 17th and 18th century, is that of rational and, especially verbal thought. Philosophy and psychology (which grew from philosophy at the end of the 18th and during the 19th century) have maintained this focus on verbal thought and for the most part ignored other forms of thinking.
As an effect, both the general public and scholars think of thought as being in the form of words and, therefore, capable of being expressed in words without any loss of content. Conversely, if you find yourself unable to express your thoughts, you think of yourself and may be perceived as lacking clear thinking or verbal competence.
That, in my opinion, is a misconception.
Because, while there may be people who are very verbal and rational, there are certainly many people who have other things going on in their minds besides words. I, for example, think in images, emotions, body perceptions and other sensory registers. When I consider a problem and its solution, I don't always use words in my mind, and certainly not logic, and if I do, these verbal thoughts are always supplemented by those other kinds of thinking.
But since Western communication largely relies on verbal expression, and since it is difficult to translate many of these non-verbal thoughts into words, the result is that I find it hard to say what I think, and that others find it hard to understand what I mean.
This need not be a problem in face-to-face interaction, though. There is non-verbal communication. You can hug someone, cook them a great meal, or create art. All of which are communication and an expression of thought.
Once you stop thinking of thought and communication as merely verbal, you can begin to find ways of ordering your thinking without translating it into words, and ways of expression that don't rely on words alone.
The statement that "a picture says more than a thousand words" is true, you know.
This is not a direct answer to the question, but a related construct that may be useful is alexithymia.
Alexithymia is a personality construct describing relatively decreased ability to identify and express emotions. Psychometrically, the alexithymia construct has seen extensive use and undergone testing that by and large supported its validity (Bagby, Parker and Taylor, 1994a; Bagby, Parker and Taylor, 1994b). In clinical populations, the causes have been theorized to include anterior cingulate cortex and right hemispheric dysfunction, but the cognitive neuroscientific evidence is currently mixed (Zaidel, 2005).
Unfortunately, I am not aware of any direct parallel for the inability to adequately express thoughts, nor of any direct treatments, and I was not able to find anything in the literature. Hopefully, the alexithymia construct may still be of some use in finding an answer.
Bagby, R. M., Taylor, G. J., & Parker, J. D. (1994). The twenty-item Toronto Alexithymia Scale—II. Convergent, discriminant, and concurrent validity. Journal of psychosomatic research, 38(1), 33-40.
Zaidel, G. T. E. (2005). Alexithymia, interhemispheric transfer, and right hemispheric specialization: a critical review. Psychother Psychosom, 74, 81-92.
