"You aren't gonna need it"[1][2] (YAGNI)[3] is a principle which arose from extreme programming (XP) that states a programmer should not add functionality until deemed necessary.[4] Other forms of the phrase include "You aren't going to need it" (YAGTNI) [5][6] and "You ain't gonna need it".[7] Ron Jeffries, a co-founder of XP, explained the philosophy: "Always implement things when you actually n