For an average Japanese, however, avoiding non-listed kanjis is impossible. A lot of non-Jōyō characters are mixed into everyday texts; novels, magazines, personal communications, technical materials. Basically, people outside the government, the press or education do not care if the character they are going to write is in a table. True, 羨ましい is less used than うらやましい but I find "SHOULD BE avoided" too didactic to describe a mere tendency.that kanji is not on the jōyō kanji list, to put it another way, kanji that are left in the cold SHOULD BE avoided
Writing 羨ましい is not a social faux pas. Your friend may find your letter uptight if you use too many difficult kanjis but one or two do does not raise the alert. What is perceived as a difficult kanji is related to the table but we do not directly draw upon it.羨ましい in the letter for Japanese friends without being frowned upon, right?