Why is this the answer?

The answer is habit because this tricky puzzle is actually a clever word game hiding in plain sight. It is a word that describes something everyone has, and that is why the riddle starts by saying, "I have one, you have one." A habit is something you do regularly, like reading a book every night or always cleaning up your toys without needing to be told. The real fun comes from playing with the letters in H A B I T. The riddle gives you three clues that are also hidden words within the remaining letters. Let's look at the first clue: "If you remove the first letter, a bit remains." The first letter of H A B I T is H. If you take H away, the letters left are A B I T. See how the words "a bit" are spelled out right there? It's a sneaky way of telling you what letters will be left over. The second clue says, "If you remove the second, bit still remains." If we take away the second letter, which is A, the remaining letters are H B I T. Can you spot the word "bit" in those letters? Yes, B I T is hiding there! This is another part of the word game that makes the riddle so smart. The final clue follows the same trick: "If you remove the third, it still remains." The third letter in the word H A B I T is B. Once we remove B, the letters we have left are H A I T. If you look closely at those last two letters, I and T, you will see they spell out the word "it." Because the word H A B I T works for all three clues when you take away the first, second, and third letters one at a time, it is the perfect solution. The riddle is a brilliant piece of writing that uses simple letters and common words to play a fun trick on your mind. You have to think about the letters, not just the meaning of the words, to solve this kind of puzzle.