It’s easy to love to hate the eternal optimists among us — the glass half-full, sunny side up, jolly bundles of joy who find the answer to every problem in a perpetual smile.

We hate these people. What right do they have to be so cheery?

Considering the time-honored human tradition of automatic suspicion, if not downright exasperation, toward these people, it’s quite an accomplishment that Mike Leigh’s Happy-Go-Lucky is such a winning film — after all, its protagonist may just be the most relentlessly happy fictional character ever invented.

Sally Hawkins (Vera Drake, The Painted Veil) stars as Poppy, a primary school teacher in London who doesn’t let anything get her down. When her bicycle gets snatched from outside the bookstore where she is browsing, she simply laments the fact that she never got a chance to say goodbye. Predictably, Poppy is the kind of person who provides a constant stream of frustration for most of the people in her life, but surprisingly, not for the audience.

Equal credit belongs to Hawkins and writer/director Leigh for the tension between charming and obnoxious they so adroitly balance. Hawkins doesn’t hold back on the sanguine levels and Leigh gives her free rein to do so, but this is a screenplay that isn’t as blithe and feather-light as it appears.

Leigh, known for his social realism works like Naked and Vera Drake, fills out Poppy’s universe with a host of characters much more in touch with their miserable side – her roommate despairs of ever finding love, her driving instructor has severe anger issues, and her pregnant sister doesn’t mind stepping on everyone around her, not least of all her timid husband.

The film functions as a series of episodic vignettes featuring these characters, and it’s linked together more thematically than plot-wise, with a counterpoint to Poppy’s cheerfulness around every corner. The real joy of the film comes through in these contrasts – it keeps Poppy from becoming a one-note Pollyanna and it allows the movie to find grounding. Happy-Go-Lucky features a number of scenes that rely heavily on improvisation, and it gives the audience the sense of watching real people interact. Polly is made familiar, and perhaps that is why her bubbly demeanor isn’t grating, but welcomed.

Happy-Go-Lucky belongs to Hawkins. She owns every scene she is in, but it’s the supporting characters – the rain to her sunshine – that add depth to this warm and inviting film. After all, how would we know what happiness looked like if a glum counterpart didn’t exist? Eddie Marsan (V for Vendetta, The Illusionist) is pitch-perfect as the latent rage-bearing Scott, and it’s his uptight driving instructor that most exemplifies this disparity.

This rambling and loosely structured film unfolds leisurely, but it seems to be urging us to take the route Poppy would. Don’t get frustrated; don’t get uptight. Just sit back and try to enjoy. And, even if you hate it, I doubt it would bother her one bit.