A metaphor for how to get started in turning around a project is catching up on e-mail after an extended absence such as a vacation. The way I deal with this situation is I start with what I can control, which is the e-mail I receive the day I return. This ensures that the backlog doesn't get any worse while I work on older messages. I will first look for recent high-priority messages and deal with those. Then, as time permits, I will start by deleting (without reading) messages that are clearly junk or out of date. I will then look for mail threads (i.e., multiple messages with the same subject) and start by reading the most recent message on the thread. In most cases, I can then delete all the older messages and be caught up on the subject. By the time I've finished this process, very few messages will be left, and life will be back to normal because I'll be caught up.
Moving to a culture of sustainability is obviously not the same nor is it as simple as dealing with an e-mail backlog. However, if you are able to recognize that you need to start with what you can control, know where you want to end up, and have an understanding of the steps you can take to get yourself out of the current situation, then the change scenario becomes more plausible. You can't try to solve everything at once, and you need to think about the problem in understandable increments that keep you on the desired path. Change initiatives will fail if they attempt to boil the ocean or lack focus or a clear sense of first steps and overall vision.
Think of your organization as a supertanker; it is big and takes a long time to change direction. Given that you know where you want to end up, recognize that you can't make the entire turn at once. Instead, what are the things you can do at any point in time that nudge the supertanker in the desired direction?