What comes once in a minute, twice in a moment, but never in a thousand years?

The correct answer is the letter 'm' because it is the only letter that appears once in the word "minute," twice in the word "moment," and not at all in the phrase "a thousand years." This riddle plays on the presence and absence of specific letters in various words, encouraging lateral thinking rather than straightforward computation. The challenge lies in recognizing that the question is not about time but rather about the characteristics of language and spelling. Understanding this subtlety is essential for solving riddles of this nature, where the focus is on wordplay rather than numerical values or factual knowledge.