Being happy or being miserable, or, if you're not happy, having hope or not.

the answer varies from day to day

Hope

Having enough of it all vs. not

Difficult question. I'd say it's whether or not you have the certainty of feeling a minimum of happiness/comfort in the near future.

Momentum. It is momentum that carries us over the pitfalls that would stop us to live.

The concentration of certain neurotransmitters in your brain