Is it really a custom not to enter the ancestral grave without a son?

A bachelor who has never been married in his life cannot enter the ancestral grave. It was said in ancient times that there will be many bachelors in the future. A man who marries and has children but has no son is not allowed to enter the ancestral grave after death. So in the old society, if there were no sons in this life, he would take his brother's son as his own son. This is called adoption. After adopting a son, he can be buried in his ancestral grave after his death.