The phrase ‘thinking outside the box’ has aged well, but it has aged. A Wikipedia entry suggests it could date back to the 1880s. Or that it may have gained traction in the business world sometime in the 1950s. Regardless, it persists as a metaphor for that exercise where you must connect nine dots in a three-by-three grid using only four straight lines. The ‘trick’ is that the limit of the playing field extends beyond the confines of the three-by-three grid. Maybe it has become a cliché for having innovative solutions.