The screenplay is a textbook example of how to build a character arc.
As Russian Doll mania sweeps over through the United States (Check out our analysis here), it's a good time to revisit one of its biggest influences: Harold Ramis' beloved 1993 comedy Groundhog Day. Oft replicated as of late, the premise was initially an exercise on immortality. What Danny Rubin's script became, however, was something much more - a sterling example of how a simple premise can bring about organic character change.
In it's an examination of the film, Lessons from the Screenplay breaks down the exact formula on how providing a character with conflict stemming from the self and a path to overcome that internal strife can lead to a gripping story. For Bill Murray's Phil, said character flaw is that he is the most egocentric newscaster alive, yet he wants to fall in love.
How he overcomes his own self-centeredness to obtain his desire is the heart of the story. Phil wants to be with Andie MacDowell's Rita, but she won't have him unless he becomes selfless. The genius behind Groundhog Day, as LFTS notes, is how "in order to drive the protagonist to change, the script imprisons him in a place that will constantly be attacking his flaw."
So how exactly does he change?
Needless to say, he doesn't learn the first time. He tries to exploit the system, but he just gets bored. His second strategy is just as self-centered as he uses every day as another chance to learn about Rita's interests solely with the intent of manipulating her into loving him. This clearly doesn't work either.
"in order to drive the protagonist to change, the script imprisons him in a place that will constantly be attacking his flaw."
In what is perhaps his most revealing characteristic up to that point in the film, Phil would rather die than change his own self-centered ways, attempting suicide but thwarted by the boundaries of "magical realism" which the script creates.
It is only when he begins spending every repeating day attempting to make other people happy, that he himself becomes truly selfless and happy. As a result, he achieves his desire and is released from the trap.
It is the strength of Phil's character arc that ultimately makes the film so effective and timeless. The movie is a demonstration of how we can work the formula of "character's flaw + change = the character achieving what he desires."
The circumstances and boundaries in between are how you can make your project your own.