"Hinc illae lacrimae" (Latin for "hence those/these tears") is a line from the Roman poet Terence's well-known comedy, Andria (166 BC).
The phrase has, since the era of the Roman Republic, been appropriated for use as a popular saying or quotation[1] to be employed when a previously-obscured reason or explanation—for some action(s) or behavior—is recognized; and, especially, when a baser motivation is thereby identified, contra an (initially-assumed) nobler one.
[2] In line 126 (Act 1, scene 1) of the comedy Andria (known in English as The Woman from Andros), Terence has character Simo, commenting to interlocutor Sosias, on the tears of his son—Pamphilus—at the funeral of a neighbor.
At first, Simo assumes that they indicate his son's sympathy for the departed, and is pleased that Pamphilus is so evidently noble-hearted; but, upon seeing that the funeral procession includes the deceased's pretty younger sister, and realizing that his son's "grief" is only feigned in order to get closer to her, erupts with: Hinc illae lacrimae, haec illast misericordia!
[5][6] This relatively early appropriation by eminent Roman authors, along with the initial and enduring popularity of the play itself, has led to the phrase becoming a familiar quotation in the Western cultural sphere.