If you subscribe to a notion of free will - that we are architects of our own destiny rather than slaves to unseen forces - which in itself would be an act of free will, then it's easy to fixate on the never ending jumble of what ifs.

What if I had worked harder at school; what if I had chosen another profession; what if I had taken a leap of faith and said, "I love you"; what if an actor other than Daniel Radcliffe had been cast in Michael Dowse's romantic comedy?

Casey Affleck was reportedly interested in playing the film's emotionally bruised hero but eventually passed on the role.

It's our loss.

Radcliffe allows some of the woodenness of his Hogwarts years to creep into his portrayal of a medical school dropout, who stumbles upon love when he least expects it.

On-screen chemistry with the luminous Zoe Kazan simmers pleasantly but never reaches boiling point, diminishing our investment in the characters as they struggle to overcome the fear of rejection and verbalise their churning emotions.

With a different lead actor, who allowed the laughs in Elan Mastai's script to build naturally rather than forcing them, What If could have been an emotionally richer, funnier and sexier slice of modern day twenty-something angst with the potential to usurp the genre's reigning champion: (500) Days Of Summer.

Wallace (Radcliffe) is disillusioned with love, convinced that he will never meet a significant other like his kooky roommate Allan (Adam Driver), who intends to marry his sweetheart, Nicole (Mackenzie Davis).

"In fairy tales, love inspires you to be noble and courageous," opines Wallace, "but in real life, love is just an all-purpose excuse for selfish behaviour."

Vowing to steer clear of romance, Wallace seeks refuge in the company of his sister Ellie (Jemima Rooper) and her son Felix (Lucius Hoyos).

At this low ebb, Wallace encounters talented animator Chantry (Kazan), who lives with her longtime boyfriend Ben (Rafe Spall).

Chantry and Wallace become good friends but both secretly acknowledge a spark of attraction that could be fanned into a full-blown affair.

As they wrestle with unspoken desire, Chantry's sister Dalia (Megan Park) makes a play for Wallace.

This unexpected attention piques Chantry's jealousy and forces uncomfortable truths into the open.

What If follows a time-honoured romcom recipe and has many of the ingredients to delight but Michael Dowse's lightweight confection fails to rise properly.

While Kazan eases into her role, Radcliffe is an awkward fit and his comic timing is slightly off throughout.

Outlandish stretches of credibility in the final act certainly don't help but screenwriter Mastai has an ear for snappy dialogue than ensures plenty of smiles if not quite guffaws.