One reason it would fail is if you have no internet connection. Another thing that is kind of odd, and I don't know why or how it would affect it, but before the "Select and Install software" step, there is also a option asking if you want to allow them to know what packages you select, I think they call it the "popcon",
https://popcon.debian.org/ A strange thing, in the past , when I was trying to install Debian, if I selected NO, and did not want to participate, the installation failed, at the "Select and Install software" step, so when I tried again, I selected YES,... and the installation proceeds smoothly. Don't ask me why it is like that, I don't know.
But on more then one occasion, the same thing occurred, and the same, when I selected YES for the popcon option, it went on smoothly and installed the packages I selected.
Some more and better details would help, IE, like exactly step by step, what you do in the install, and also specifically, which ISO / version of Debian you are trying to install, ? netinstall ?, DVD, or ????