It looks like Park Seo Joon made a good decision to use this stage name of his!
During the June 6 broadcast of a Beeteem TV variety program, a Believe It or Dont Believe It Tuesdays Fortune (literal translation) corner featured philosophy professor Jo Gyu Min, who utilized the five elements—wood, fire, earth, metal, water—of Eastern philosophy to analyze the stage names of various celebrities.
He named Park Seo Joon as having made the best choice, as his stage name would manifest as earth-earth-metal in the five elements, a harmonious combination. However, the actors real name Park Yong Gyu would be earth-water-wood, an incompatible relationship. Therefore, Park Seo Joon is a better name based on this analysis.
However in Sullis case, he explained that both her real name (Choi Jinri) and stage name appeared to be incompatible with her person. As for both Seo Kang Joon (real name Lee Seung Hwan) and Block Bs Zico (real name Woo Ji Ho), the professor deemed that their real names were much better in comparison to their stage names.