People forget that James Cameron movies historically have long legs.
This is a 3+ hour movie. That cuts into the number of showings AND people's willingness to see late shows. My local theater is pretty much sold out tonight for early shows but not for showings that get out at 2:00 am.
This was never going to open the way a Star Wars or Avengers movie would. From the reduced choices of good viewing times, from a desire to see it in the best possible theater, from a lack of rush to avoid spoilers that other franchises are known for, there are many reasons not to discount the film's performance yet.
Time will tell but judging the success of a James Cameron movie based solely on the opening weekend is just a bad choice, given his history.
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