If a theory cannot be disproven, what aspect is it lacking according to Daniel's teacher?

The theory's lack of disprovability indicates that it is missing the quality of falsifiability. Falsifiability is a critical aspect of scientific theories because it allows for the possibility that the theory could be proven wrong through evidence or experimentation. If a theory cannot be tested or potentially disproven, it remains outside the realm of scientific inquiry, as it cannot be subjected to scrutiny or validation through empirical data. The strength of a scientific theory lies not just in its ability to explain phenomena but in its openness to being challenged and refined based on new evidence. Thus, a theory that lacks falsifiability cannot contribute meaningfully to the scientific process.