Final answer:
The mass a star is formed with is the primary determinant of how it will differ from other stars, affecting its evolution, lifespan, and behavior.
Step-by-step explanation:
The characteristic that most determines how stars will differ throughout their lifetimes is the mass they are formed with. Although all stars begin with a similar basic composition, it is their masses that govern the pace at which they evolve through their life stages. Stars with greater mass will burn through their nuclear fuel more quickly, resulting in a shorter life span and more energetic end-of-life phenomena, such as supernovae.
For example, massive stars on the main sequence have high temperatures and high luminosities, while low-mass stars have lower temperatures and luminosities. Furthermore, the range of possible behaviors a star exhibits as it ages can vary widely according to its mass, composition, and whether it has any companion stars nearby. Understanding these differences is crucial for tracing the evolution of stars from birth to death.