I don't want some pretty face to tell me pretty lies

A beautiful flower may hide a painful thorn, but it can't be hidden forever. Once it is exposed, the flower loses a part of its value. The thorn may be removed, but whoever holds the flower will forever be suspicious of other potential thorns. Time may pass in which no other thorns are found on the flower, but a simple imperfect bump on the stem can be perceived as a thorn to the wary eye. Thus the thorn suspicion is reinforced, and any trust that the flower gained is lost once again.