${?}_{{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_r\text{e}\text{f}\text{e}\text{r}\text{s}to\text{t}\text{h}\text{e}\text{t}\text{e}\text{n}\text{d}\text{e}\text{n}\text{c}\text{y}of\text{s}\text{y}\text{s}\text{t}\text{e}\text{m}\text{r}\text{e}\text{q}\text{u}\text{i}\text{r}\text{e}\text{m}\text{e}\text{n}\text{t}\text{s}to\text{c}\text{h}\text{a}\text{n}\text{g}\text{e}\text{o}\text{v}\text{e}\text{r}\text{t}\text{h}\text{e}\text{l}\text{i}\text{f}\text{e}\text{t}\text{i}\text{m}\text{e}of\text{t}\text{h}\text{e}\text{d}\text{e}\text{v}\text{e}\text{l}\text{o}\text{p}\text{m}\text{e}\text{n}\text{t}\text{p}\text{r}\text{o}\text{j}\text{e}\text{c}\text{t}\text{.}}$

${?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}$refers $to$ the tendency $of$ system requirements $to$ change over the lifetime $of$ the development project.

Feature creep

Optimistic design

Silver bullet syndrome

Requirements gold$-$plating