Why does it make it difficult for astronomers to understand the later stages of stellar evolution?

Astronomers find it challenging to understand the later stages of stellar evolution primarily because these phases are often short-lived on a cosmic timescale, making it difficult to observe them directly. Additionally, many stars undergo complex processes, like supernova explosions or the formation of neutron stars and black holes, which are not easily modeled or predicted. The extreme conditions and varied outcomes in these late stages further complicate our understanding, necessitating reliance on simulations and indirect observations. Consequently, much of our knowledge is based on theoretical models rather than direct evidence.