Symbolism, Imagery, Allegory
Just after our boy Pericles survives a shipwreck and washes up on the shores of Pentapolis, a bunch of fishermen haul out a set of rusty armor that was given to him by his (dead) father. The armor is important to Pericles because it's a precious family heirloom, and he sees it as a link to his beloved dad: "He loved me dearly, /And for his sake I wish the having of it" (2.1.138-139).
The armor washing up on shore is also totally convenient because now Pericles can go to King Simonides's jousting tourney, bump some knights off their horses, and win the heart of the local princess. When Pericles shows up at the jousting tournament wearing some janky armor, it takes on even more meaning: the knights have no idea he's a king and just assume that he's got no game because he looks more like a cart driver who uses a "whipstock" than a knight who uses a "lance":
He had need mean better than his outward show
Can any way speak in his just commend;
For by his rusty outside he appears
To have practised more the whipstock than the lance. (2.2.48-51)
Clearly, nobody has ever told these guys that you can't judge a person based on appearances alone. While the knights stand around and rag on Pericles's rusty armor, King Simonides actually says something smart: "Opinion's but a fool, that makes us scan / The outward habit by the inward man." In other words, he isn't ready to judge Pericles's inner worth based on the guy's outward appearances. That's some pretty solid advice, don't you think? Check out "Themes: Deception" if you want to think about this idea some more.