When things get complicated, they are no longer simple and straightforward. If you are asked a question that would require a long, detailed answer, you might just say, "It's complicated."
The word complicated came about in the 1640's to mean "tangled" or "difficult to unravel." This makes sense, considering it came from the Latin verb complicāre, meaning "to fold together." Consider that something with many folds is more complicated than something flat. Novelist Robert Ludlum said, "Life is extremely complicated," but Confucius long ago suggested that "Life is really simple, but we insist on making it complicated." Just having those two opposing viewpoints indicates how complicated life can be.