Why do chance events play a role succession?

the answer is: certain species may show up early or late in the process, or not at all

Succession refers to the process that occurs when organisms evolve and adapt to its environment overtime.

Different type organisms tend to have different genetics that determine their success rate to survive in a certain type of environment. This means that chance/luck play an important role among those organisms because organisms that are born at the correct place or correct time might have a higher chance of survival.

For examples, humans have higher chance of survival if we are born today. But, if we are born in the time when dinosaurs still exist, we would have a really low chance of survival.