All indications are that tonight's episode,"The Variable," will be the long awaited Daniel flashback episode which should fill in some of the blanks on all the time travel machinations of the Island and, hopefully, we'll get a bit of backstory on Daniel's mom as well.
So one question for tonight is what is the variable? The easy, quick answer to this is Daniel, since it is his episode and Desmond has already played the role of the constant before. But perhaps a better question is what is the equation instead? "The Constant" was referring to the rules of time travel itself, i.e. one needs a constant through the time periods when one's consciousness travels through time. But I'm thinking tonight's episode might refer to the ultimate solution to the show itself.
Perhaps Daniel, who essentially figured out a way to time travel on his own, is really the key to finding a somewhat happy ending to Lost. After "Flashes" aired, I guessed that Lost would end with Desmond going back in time to save everyone with no hope of getting back to the future. Penny then volunteers to go with him and they end up becoming Adam and Eve. Since then, considering we haven't seen Rose and Bernard since everyone started time traveling, it seems a lot more likely they're really Adam and Eve instead.
But let's say Daniel is a metaphorical variable to the end of the show. How could he affect things? Originally I thought Desmond was going to be a fluctuating wild card when it comes to time travel, possibly able to break the rules of the equation itself. And while that may still be true, perhaps Daniel is going to play an equally important time traveling role, something akin to a master course corrector. Desmond seems to need a lot of course correcting to get him to where he needs to be, with Daniel's mom having taken primary responsibility up until now. But maybe from here on out it will be Daniel's job instead.
Expectations are high for tonight. It's going to be hard for tonight's episode to match "The Constant" simply because Desmond and Penny have a wonderful relationship to build an episode around. But one of the biggest knocks on this season has been the relative paucity of Daniel screentime. That gets corrected tonight! Enjoy the show! Review up tomorrow morning! :)