The amount of your ancestors increases with each generation
you have 2 parents, 4 grandparents, 8 great-grandparents, 16 great-great-grandparents etc.
so let's say there are 3 generations per 100 years
so it gives us 30 generations in 1000 years
which means 2^30 = the number of your ancestors who lived in year 1000 would be over 1 billion people which is impossible
explain this to me