You may or may not have noticed this, but the human being is capable of feeling a wide range of emotions.
Far wider than the range of words denoting emotions available in the vocabulary of an ordinary person.
Quick! What's the word for the feeling of remembering a heartache felt on an autumn afternoon faintly scented by the promise of resumed rain?
There is no such word.
If you are of the creative kind, you might very well have made up a word for this in the time between reading this line and the line above this one. If so - then good for you. It is a useful word.
Humans are peculiar creatures. They tend to feel something as a baseline feeling for an extended period of time, and to afterwards go around and remember/refeel this from time to time. Oftentimes, they use the rememberances of these baseline feelings as an unarticulated emotional backdrop which everything newly encountered is compared and contrasted to.
They never give words to these feelings, though. And thus never get around to the all-important task of getting to know themselves.
There is a feeling of sadness associated with this thought. There is, however, no word for this feeling.
Now might be a good time to change this.