3. Trading Randy Arozarena
This decision sticks out above the rest. For years, the Cardinals have had a severe logjam in their outfield that has led them to trade players who became stars or hold onto players who didn't quite take off.
The most famous example is the Randy Arozarena trade back in January 2020. St. Louis sent him and Jose Martinez to the Rays in exchange for Matthew Liberatore.
The deal did not work out in the Cardinals' favor, as Liberatore has not performed well in the Major Leagues. Meanwhile, Arozarena broke the record for the most home runs in a single postseason and earned Rookie of the Year honors in the American League the following season.
This deal is talked about ad nauseam, probably more than it should be at this point, especially considering that Yordan Alvarez was once a prospect in the Dodgers system before being traded to Houston.
Still, it's a trade that negatively impacted the Cardinals, who are now stuck with several underachieving outfielders, namely Tyler O'Neill, Dylan Carlson, Juan Yepez, and Alec Burleson.
Had the Cardinals kept Arozarena, their 2020 season, while shortened might have gone a little bit better and they could have made a deeper October run with the young star on their side.
Plus, having Arozarena in the outfield with Lars Nootbaar and Jordan Walker would certainly help, as Arozarena is an elite defender and has a cannon for an arm.
But this trade still haunts the Cardinals almost four years later.