How to avoid having injector.createInstance() all over the place when using guice?

There's something I just don't get about guice: According to what I've read so far, I'm supposed to use the Injector only in my bootstrapping class (in a standalone application this would typically be in the main() method), like in the example below (taken from the guice documentation):

public static void main(String[] args) {
    /*
     * Guice.createInjector() takes your Modules, and returns a new Injector
     * instance. Most applications will call this method exactly once, in their
     * main() method.
     */
    Injector injector = Guice.createInjector(new BillingModule());

    /*
     * Now that we've got the injector, we can build objects.
     */
    RealBillingService billingService = injector.getInstance(RealBillingService.class);
    ...
  }

But what if not all Objects I ever need can be created during startup? Maybe I want to respond to some user interaction when the application is running? Don't I have to keep my injector around somewhere (e.g. as a static variable) and then call injector.getInstance(SomeInterface.class) when I need to create a new object?

Of course spreading calls to Injector.getInstance() all over the place seems not to be desirable.

What am I getting wrong here?