Many laws work like that. They don't have very precise definitions of things, but instead depend on what an average, reasonable person would think.
An example of this is contract law. There is no clear definition of what a legal contract must look like. Instead, a contract's validity can depend on whether an average, prudent person would have entered into it in similar circumstances.
An example of this is contract law. There is no clear definition of what a legal contract must look like. Instead, a contract's validity can depend on whether an average, prudent person would have entered into it in similar circumstances.