Once you’ve established who the main character is and what their main trait or weakness is, the next thing to make clear in the logline is what’s driving this character, what they want or need to achieve.
The type of goal depends on the kind of film. In an action-driven film, the goal will often be concrete and easily described, e.g., the main character must defuse a ticking bomb, retrieve a magic ring, prove his client’s innocence, escape the psychopathic killer, and so on. In a more internal, character-driven story, the main character will often be trying to avoid some aspect of themselves due to fear. They may be not even be aware of what they really want until very late in the film. Of course in an action film, the main character also tries to avoid some aspect of themselves, and in a character-driven story the main character must also undertake something concrete. So it’s not a black and white distinction, rather a matter of emphasis.
Generally speaking, the main character has to do something difficult, unpleasant or frightening in order to achieve the ultimate goal.
The logline must reflect the main narrative drive of the film in a simple, easily comprehensible way. One of the most effective ways to describe succinctly what the film is about is to sketch the chief dilemma or danger into which the main character is thrown.
Describe what the main character has to do in the simplest possible terms, but using words which show the character has no choice but to follow this path, even though they would actually rather not. The main character must ... or is forced to ... or struggles to ... undertake some kind of activity, in order to achieve what it is they (think) they want.
An affable, bourgeois psychotherapist struggles to come to terms with the accidental death of his teenage son ... (The Son’s Room). The conflict and contrast is there in a nutshell: he’s a nice, well-educated, family man who wouldn’t hurt a fly, and his son is killed. Bam. His life is turned upside down and his seemingly unattainable goal is to make sense of what has happened.
An absent-minded but well-meaning ant ruins the colony’s harvest and must redeem himself by finding help in the hostile outside world ... (A Bug’s Life). The poor ant is sent on a mission impossible because of a mistake he made. He has no choice (although he thinks it’s his decision) and will obviously face great dangers for which he is totally ill-prepared. His aim is to make up for his mistake.
When his wife is brutally murdered, an exemplary young British diplomat in Africa, becomes obsessed with identifying the killers and their motive ... (The Constant Gardener). Here is a man whose life is expected to follow a very predictable and probably hypocritical path, but suddenly his focus changes completely. The only thing he cares about now is uncovering the truth, even to the detriment of his carefully prepared career.
Of course, if the main character were able to achieve the goal fairly straightforwardly, the film would be over pretty quickly. So the writer puts all sorts of obstacles in the main character’s way. But more about that next time.