Adjacency List implementation of Graphs

https://online.codingblocks.com/player/7408/content/106?s=1482
In lecture videos of adjacency list implementation it is said to make an dynamic array because we dont know the vertices .
But cant we make it static as the number of vertices would be fixed so when graph is inputted than vertices would be fixed for that time
Than why to make dynamic array?

We make the dynamic array as when writing the code we don’t know how many vertices we are going to get… we will know this only at run time… so that’s why we are using a dynamic array here.