Whatever setbacks there were for Sauron, he didn't see it that way, he outnumbered his enemy, he was convinced that someone would use The Ring against him. By the time Sauron realized he was wrong, The Ring had been thrown into Mount Doom.
"Today we cover the origins of Sauron, including his time as the maia Mairon, coming to serve Morgoth, and fighting for the Dark Lord during the Wars of Beleriand."
"The story of the Second Age is one driven by its villain: Sauron. Here we see the Dark Lord use his great powers of manipulation time and again, resulting in the Rings of Power and the downfall of Numenor."