Between 1980 and 1993, the Montreal Canadiens were a consistently excellent team, winning 7 division titles. In that span, they were one of the top 6 teams in the league in points every season except for 1984, 1986, and 1993. What happened in those three seasons? In 1984, the Habs went to the Conference Finals. In 1986 and 1993, they won the Stanley Cup. The division winners weren't so lucky - six of the seven teams were eliminated in the the first or second playoff round.
This shows how the playoffs are often a crapshoot. The three worst Montreal teams in a 14 year period combined for 2 Stanley Cups and a Conference Final appearance. The seven division champion teams only once made it past the second round. How did the weak teams manage to succeed where the stronger ones failed?
One of the key reasons is playoff matchups. Obviously, teams playing stronger opponents are more likely to lose. For example, in the six years between their Cup wins, Montreal lost four times to 100 point teams, all of whom were better than they were.
In 1986 and 1993, they quite simply avoided the top teams. The best team Montreal played in the 1986 playoffs was Calgary, an 89 point team during the regular season. They beat 86 point Boston, 78 point New York Rangers, and 84 point Hartford. Sure, the Habs were only a 40-33-7 team, but they were as good as anybody they played in the playoffs.
In 1993, it was a similar story. The Habs were a solid team that put together a 48-30-6 record throughout the season, good for third place in the division. After a tough first round series against 104 point Quebec, where Montreal won three games by just a single goal, 2 of them in overtime, the Habs beat Buffalo (86 pts), the Islanders (87 pts), and Los Angeles (88 pts), all of which were clearly inferior teams.
The 1986 and 1993 Montreal Canadiens had tough, experienced lineups and all-star goaltending from Patrick Roy. But probably the most important reason that both teams won the Cup was because they had very favourable matchups. None of the 8 teams they played had more regular seasons wins than Montreal did, and none of them were elite teams, or even division winners.
Even on the Avalanche, Roy benefitted from a good "luck of the draw" in the playoffs, although that was partly because his own team was so good that they usually played lower seeds. In his four Cup runs combined, Roy only had to face three division winning teams, and the only one of them that won more games during the season than his own did was the 1996 Detroit Red Wings.
Patrick Roy was a great goaltender, but two of the main reasons he won 4 Stanley Cups were the quality of the teams he played on, and great luck in avoiding the best teams in those playoff runs. Winning with two of the weaker Hab squads has also been instrumental in creating Roy's reputation as a clutch, game-stealing goalie that wins with less than impressive teammates. However, that's not really true - the Montreal Canadiens of the late 1980s and early 1990s were excellent teams, they just happened to underachieve during the regular seasons of the years they won the Cup. Many have the perception that Roy did not play on great teams during his time in Montreal - nothing could be farther from the truth. He did not win the Cup with the best teams there (although he came close in 1989) but the Habs were consistently excellent with Roy between the pipes, which certainly helped him in the win column as well with his performance statistics.