Most things get used up. Candles, gas tanks, glasses of water, money in the bank. Other things work a bit differently, in a more biological way: rather than getting used up, there are systems that attempt to match their usage. Strength is a good example... everyone realizes that the more often you use your muscles and your physical energy, the more your body will have available for you next time you need to use it. The body tries to match the demand for its resources. The body responds to effort being used by becoming stronger. This is common knowledge, but I think that this phenomenon actually applies to more areas of our lives than we typically give it credit for.
In fact, almost everything about ourselves works this way: memory, passion, intelligence, patience, empathy, strength of will, ambition, luck, happiness. All of these things that we sort of assume are static characteristics of ourselves can be exercised and improved.
Something I've been noticing lately is that people often inadvertently discourage trying to change. People say you are forcing things, or trying too hard. People encourage you to relax, take it easy, calm down, give yourself a break. While these are meant to increase happiness, I think they are misleading in that the way to improve yourself often requires a very forced and concerted effort that in fact includes actually trying.
What are you trying to do right now. Beyond survive. Which parts of your brain and body and life and circumstances are you trying to improve? I've found that even the ability to "try" is something that takes practice, and exercise. The biggest problem is probably that it's difficult to focus on something when focusing itself is something that we don't have much natural ability in (and it only gets worse with all of our daily distractions). People don't realize how easy it is to try to do something, once you can focus on trying to. Or, they don't realize that there's a correllation between trying and actually doing. Excuses I hear a lot are that they don't know where to start, or that it's not that simple. A lot of people seem to be happy being unhappy. I find it a bit ridiculous. Why must a job "be a job"? Why must compromises be made so quickly? If compromises must be made, at which point should they be made? I think amazing things happen to people who expect amazing things to happen.