Portraying everything from childlike wonder to wartime drama to social commentary on parenting — and even “careful what you wish for” warnings about the price of fame — “Goodbye Christopher Robin,” the new biopic detailing the life of British author A.A. Milne and his classic “Winnie the Pooh” children’s stories, truly has it all. And that’s precisely the problem.

As it explores the beautiful yet complicated father-son relationship between Milne (a game Domhnall Gleeson) and son Christopher Robin (newcomer Will Tilston), Milne’s unlikely muse, “Goodbye Christopher Robin” is a tale that teeters back and forth between heartwarming and cautionary, never deciding which it is. The result is an identity crisis, rendering what could have been a great film effective only in fleeting spurts.

“Goodbye Christopher Robin” begins just after World War I, when Milne, having returned safely home from battle to his native England, sees his creativity and happiness hampered by lingering PTSD. Against the wishes of his wife Daphne (rising star Margot Robbie), who relishes the pleasures of high society that she and her affluent husband enjoy, Milne moves the family from London to the sedate Sussex countryside in hopes of clearing his mind and writing a searing literary work “to end all wars.”

When Daphne gives birth to baby boy Christopher Robin, whom she and Milne affectionately call “Billy Moon,” Milne hires Scottish nanny Olive (a great Kelly MacDonald) to prevent distractions from his writing process. It isn’t until a few years later, however, when Olive is forced to leave town to tend to her ailing mother — while Daphne indulges in a long stretch of partying in the city — that Milne discovers his greatest inspiration while looking after his inquisitive son.

So lucid is Christopher Robin’s imagination and so contagious his innocent sense of wonder when he plays with his stuffed animals in the forest surrounding their home, that Milne believes it could be the source of the next great children’s book. As history has proven, Milne’s prediction was right on the money. He and his illustrator Ernest (Stephen Campbell) capture the magic of Christopher Robin at play via “Winnie the Pooh,” which goes on to become an international phenomenon.

Undoubtedly, the highlight of “Goodbye Christopher Robin” is Tilston’s utterly adorable performance as Christopher Robin. You’ll be charmed and engaged as you watch the wide-eyed boy play with his stuffed animals, ask his parents and nanny questions about the world around him and find joy everywhere. His energetic role is backed by fine performances from the ensemble; Gleeson, Robbie and MacDonald all appear to be fully invested in the proceedings.

However, the performances outside of Tilston’s are ultimately muddled by the film’s combating narrative elements. It’s difficult to discern whether the film’s shortcomings are the result of screenwriters Frank Cotrell Boyce and Simon Vaughan being overly ambitious in covering the real-life events or director Simon Curtis not being ambitious enough in narrowing the film’s focus. Either way, the film’s imbalanced script, though certainly not without its triumphs, stumbles toward a finish line that had the potential to be a real tearjerker, but falls short.

The handful of moments during which “Goodbye Christopher Robin” (which is rated PG) truly works leaves me convinced that, buried somewhere deep in this Hundred Acre Wood, there’s a great movie that the origin story of “Winnie the Pooh’s” truly deserves. Unfortunately, due to its inability to plant its flag in the soil and affirm its identity, “Goodbye Christopher Robin” just isn’t it.