The answer to the riddle, "What is always coming but never arrives?" is, "Tomorrow." This is because on any given day, "tomorrow" is always the day coming next.
Many classic riddles use a similar twist, which makes them difficult to solve. For instance, "Poor people have it. Rich people need it. If you eat it you die. What is it?" The answer is, "Nothing." Another familiar riddle is, "I’m tall when I’m young, and I’m short when I’m old. What am I?." "A candle" is the correct response to this riddle. Another memorable riddle is, "If I drink, I die. If I eat, I am fine. What am I?" The only correct reply is, "Fire."