I thought my hippo example was good, but I'll offer some others.
Let us say I find a small bag of money. It's not richie-rich money, but it's significant. I should like to keep (and spend) the money, but I realize the rightful owner might step forward and claim it, leaving me with a substantial problem.
So, I put flyers out about finding the money, I put an ad in the paper, I inform the police about what I've found... ad nauseam. A few years go by and there is no response. As the time passes, my belief that there is no rightful owner for the money begins to grow. At some point, my belief in the non-existence of an owner (and remember, abandoned money also lacks an owner). Surely, by whatever exhaustive method I use, I eventually have a justified belief that there is no owner at all and I can keep the money?
Now, accepting that I have a justified belief in the non-existence of a rightful owner, I spend the money. Not only do I act on my belief, but the non-existent thing directly influences my actions. If an owner exists, I'm screwed. There are direct consequences of something that doesn't exist on me, and by extension, the world at large.