There are several possible sources of open states. Here are two:
Stimulus states are open states that originate as a reaction to a present object, situation, or thought (a stimulus). For example, if you are afraid of dogs, a fear state may arise in response to merely seeing a dog. It may be difficult to leave the fear state; if so, it is a sink. Animals were more dangerous for hunter gatherers than for modern humans, and for some people this fear results in a sink state.
Exploration states involve following arrows to get from one state to another – including the creative imagination of new state elements. Exploration can include anticipation, free association, problem solving, rumination, analysis, or overthinking. For example, you may vividly imagine being attacked by a dog even if no dog is present.
Nexus State Theory 