What happens when there is a concept or element in the Target Domain that has nothing corresponding in the Source Domain?
What does this idea about love have to do with journeys?
This, I think, is more serious than an Extra Source Element. If you buy Conceptual Metaphor, the lack of anything in the source domain will make problem-solving harder because that's where you do (much of) your thinking. If there's nothing corresponding to *concept7<sub>t</sub>*, you're likely to overlook it (because you're not so much looking over there on the left).