Great reply in this thread:
Marino didn't win a Superbowl because he as a quarterback was not capable of it.
Marino inherited one of the best organizations in the league, a Miami Dolphins team that won 141 games, two Superbowls, and ten other playoff games before they drafted him in 1983. In his career he won just eight playoff games (with ten losses) and finished with a career completion percentage of 59.4%.
Claims Marino had no run game or defense are false - he inherited one of the best defenses and best run games in the league; his run game in yards per carry through his career exceeded all but eleven Superbowl champions; he had top-12 scoring defenses seven times and had the top scoring defense in 1983 and 1998; his 1984 Superbowl run came with a defense seventh in scoring with only 3,200 passing yards allowed and with a plus-eight turnover differential. By no standard could that squad be considered inferior, and all his playoff teams were good enough to go somewhere in the playoffs.
It was in the playoffs that Marino was completely in over his head, throwing at least two interceptions in nine of his ten playoff losses - in his one Superbowl he threw two interceptions, had a pedestrian 67 passer rating, and this against a 49ers team that was far from invincible (as the NY Giants and Minnesota Vikings would graphically prove the next few seasons).
The blunt truth is Marino was one of the worst playoff quarterbacks in history.
http://www.quora.com/Great-Athlete-Debates/Why-didnt-Dan-Marino-NFL-QB-win-a-Super-Bowl