What you have matters more than what you lack (If you’ve got a bicycle, consider what you can build based on that, rather than worrying about not having a car, a truck, a metal shop.)
To dwell on what you don't have stops all action in its tracks. While some things are necessary to think and act on not having (i.e. resources like water and food) one should figure out how to use what one has to get what one needs. This really spoke to me because of my surrounding culture. Here in the US everyone seems to be focused on getting the newest thing that is popular now; there is almost no thought on how to be innovative with what we already have, when a problem arises we all seem to crave new technology that can fix it rather than employing tried and true methods.