Why can the shorter reading sometimes be preferred in New Testament textual criticism?

In the field of textual criticism, the principle that "the shorter is preferable to a longer" reading is a standard canon used to evaluate manuscript variants.1

This preference is based on the observation that scribes and copyists were more likely to add to a text than to remove from it. Over time, as manuscripts were copied, there was a natural tendency for scribes to "smooth" or clarify the text to make it easier to read or to harmonize it with other passages. This process of correction, interpretation, or stylistic expansion often resulted in longer, more polished versions of the original text.1

Consequently, textual critics often view a shorter, more difficult, or less polished reading as more likely to be the original, as it is less probable that a scribe would intentionally delete information or create a more difficult reading where a clearer one already existed. This approach is part of the broader eclectic method, which evaluates internal evidence to approximate the original historical texts.1