Answer:
What kind of pet always stays on the floor?
A morbidly-named body of water
I am a good state, there can be no doubt of it; But those who are in, entirely are out of it.
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
What is always coming but never arrives?