I think the premise is that all the miracles and testimony in the NT can't be mistaken. So, it's either truth or fabrication.Lewis’s argument that Jesus must be either Lord, Liar, or Lunatic—often referred to as the trilemma—appears in Mere Christianity (1952). This kind of breakdown in reasoning often fails because it oversimplifies real-world possibilities to just three. It constitutes a false trichotomy.
Here is a fourth possibility. From a non-believer's perspective, the story could be regarded as a legend. If the divine claims were later additions by followers, Jesus might have been a profound legendary teacher without being God, a liar, or a lunatic. Judaism views him as a rabbi and not God, while Islam regards him as a prophet. Fundamentally, non-Christians do not perceive the gospels as entirely historically reliable.
There are more possibilities. The early manuscripts might have been systematically corrupted.
Furthermore, Lewis oversimplified psychology and mental illness. Again, from an atheist perspective, someone might be delusional about their identity yet coherent in their speech. Jesus could have had a messianic self-conception—common in 1st-century Judea—without exhibiting full-blown insanity or deceit.
Consider Siddhartha Gautama who claimed to have achieved Buddhahood. Was he Lord, liar, or lunatic?
To say that he was a lunatic would only trivialize his case. He wasn't unique. There were plenty of others.
Wiki:
Sathya Sai Baba may not have been the Lord, a liar, or a lunatic (in the simplistic sense). From the atheists' perspective, he might have been genuinely self-deceived.
Another example, Wiki:
Apollo's followers do not think he is a liar or lunatic, even though non-followers may. Psychological reality is more complex than Lewis' simple delineation.
C.S. Lewis's trilemma is a memorable argument for Christians, but it has limitations for non-Christians, including Judaism and Islam. It works well within a Christian framework and for those who accept the Gospels as historically reliable. However, it does not fully address the complexities of historical criticism, cultural context, or alternative interpretations of Jesus' identity. It made assumptions that atheists would not accept. His argument is more celebrated in Christian circles than among skeptical ones. In the end, logic alone almost never converts anyone because different people use different kinds of subjective reasoning.
33As the men were leaving Jesus, Peter said to him, “Master, it is good for us to be here. Let us put up three shelters—one for you, one for Moses and one for Elijah.” (He did not know what he was saying.)
34While he was speaking, a cloud appeared and covered them, and they were afraid as they entered the cloud. 35A voice came from the cloud, saying, This is my Son, whom I have chosen; listen to him“