The word "不到" is formed by directly combining the negative adverb "不" (meaning "not") with the verb "到" (meaning "to arrive" or "to reach"), resulting in a literal meaning of "not to arrive" or "not to reach". This compound functions as a verb phrase where the negation modifies the action, typically used to express failure to achieve, attain, or complete something, such as in "看不到" (cannot see) or "做不到" (cannot do). The formation relies solely on the grammatical juxtaposition of the two characters without any phonetic or symbolic alterations.