Ari Graynor made her debut as a leading actress in For a Good Time, Call… last Friday, finally graduating from her role as the scene-stealing sidekick.

Call is a feel-good summer flick with a fun, albeit predictable, plot. Graynor plays Katie, a “sexercising” free spirit who’s facing eviction for not paying rent. Then her sassy, gay best friend sets her up with a roommate (Lauren Powell) —  who, of course, is the frenemy she made one drunken night in college. The raunchy jokes really begin when the film reveals that Katie is a phone-sex operator. The roommates’ friendship blossoms as they start their own phone-sex business.

When watching the film, it’s important to remember that this is Graynor’s first leading role, so she might have been unprepared for the larger part in Call. Much like her co-star, Graynor fails to give her character the three-dimensionality the audience craves. But, in her defense, the differences between supporting and main characters are significant enough to make her proficient at one but a novice at the other.

Supporting characters are usually the reliable friends or parents. They purposefully remain undeveloped, partially in order to keep the focus on the main characters. These secondary roles sometimes serve either as the voice of reason or as the supplement to the main character’s own conscience. In other cases, their entire purpose is to provide comedy in a film’s darker or duller moments. In an otherwise dramatic film, this allows the audience to take a breather from the heavy emotions and thick tensions.

Secondary roles are usually limited to one set of emotions, reactions and opinions: The characters remain constant throughout the arc of the story. Though two-dimensional, the role of the secondary character  is absolutely necessary.

Graynor excels in portraying these secondary roles, namely in Nick and Norah’s Infinite Playlist and Celeste and Jesse Forever.

As Caroline in Nick and Norah’s Infinite Playlist, Graynor is a hot mess, like a burnt burrito exploding with beans and cheese from the microwave. She gets drunk, she gets lost, she gets kidnapped and she steals a turkey sandwich.

Graynor is responsible for initiating the wacky plot and propelling it further as she stumbles through the film’s universe. She perfectly portrays the troublesome comedic relief, a one-sided role that, though small, impacts the entire movie. Without her antics, Nick and Norah would never bond as they search for their lost friend.

The day to Caroline’s night, Graynor’s Beth in Celeste and Jesse Forever is the best friend that forces reason back into Celeste’s emotionally turbulent life. Beth makes her friend face the reality of her relationship with Jesse, opening Celeste’s eyes to the tough decisions she has to make in order to move on with her life.

As Celeste’s life begins to fall apart, Beth is a constant force that keeps her afloat. Graynor is an exemplary foil, a fun house mirror that shows how Celeste’s life could have turned out had she acted maturely and thought through her actions. Again, Graynor plays her role with perfect consistency, the best way to depict a flat character.

Strong main characters are required to be three-dimensional with varying and contradicting opinions and feelings, internal conflicts and personal quirks. It is not enough for them to have reactions or emotions in accordance to the world around them — they must be their own moving force, a power not only affected but effective. A protagonist can stand alone, causing conflict and resolving it in one fell swoop. Most importantly, a protagonist must change as plot develops. The change might be as obvious as a complete reversal in life philosophy or as subtle as self-realization.

For these reasons, acting in a dynamic role is a much greater challenge than playing a one-dimensional character. The actor must completely understand the persona by mastering the depiction of the nuances, tics and habits that are the character.

In Call, Graynor attempts her first leading role as Katie. Through dialog and set actions, the character has all the qualities needed to be three-dimensional. Though she ultimately doesn’t change much, Katie does undergo a subtle transformation as the movie progresses.

Possibly from lack of experience, Graynor plays Katie in such a way that this change barely registers emotionally with the audience. She seems capable of only three emotions throughout the film: angry, happy and nervous. She fails to portray any subtleties of her character, showing only bigger, obvious emotions — Graynor reacts but doesn’t really act.

This worked well in her other roles simply because they required this bare minimum in order to not overshadow the main cast.

Graynor’s reacting instead of acting is most notable when Katie is by herself. When left alone, Graynor doesn’t portray any mental connections with her character. She is, in a manner of speaking, intellectually dead unless she is reacting to someone else. And even then, there are times when her responses are a bit dull.

In a pivotal scene when Katie and Lauren inevitably bond, Graynor’s eyes portray no passing emotions, no change in thought. This is the moment when the women finally connect, and though her face isn’t blank, it doesn’t emote any complexities.

Furthermore, though Graynor seemed to alter her voice to emotions with ease in her other roles, in Call, she often failed to match her sound to the events at hand. Graynor excelled with sarcastic remarks and annoyance, but when it came to more serious feelings, such as love, her hoarse voice rose in pitch and began to sound insincere. Coupled with limited facial expressions, it made for a mediocre performance.

Thrust too early into a lead role, Graynor falls short of what audiences need from a leading lady. Nevertheless, because it’s her first dip into the pool of main characters, she shouldn’t be judged too harshly. Given her firm grasp of supporting roles, hope remains that with enough practice the name Ari Graynor will one day be synonymous with leading lady.