There's a particular kind of writer who can describe their screenplay over a drink with such devastating clarity that you'd cast it on the spot. The dead mother. The reason for the silence at dinner. The object on the mantelpiece that means everything once you know the story behind it. You listen, moved, occasionally close to tears. Then you read the actual script, and half of that story simply isn't there.

The trouble is that writers are structurally the worst-placed people on earth to notice this gap, because you already know everything. You know why he flinches at the phone ringing. Your brain fills in the missing scaffolding automatically, every single time you reread the draft, which means the draft never has to prove it did the work. The audience gets no such courtesy. They arrive with nothing and leave with only what you actually put on the page.

As an art student, I was badly placed at the end of the table for a life-drawing class. The model lay along the table with his head nearest me and his body tapering away into the distance, which meant I wasn't looking at a face so much as down onto one, upside-down and foreshortened. Everyone else in the room had the easy view. Drawing a face the right way up, you already know where everything goes, the eye sits here, the nose falls this far below it, the mouth at roughly this proportion and your hand quietly starts drawing the idea of a face instead of the actual arrangement of light and shadow in front of you. Upside-down, that shorthand simply doesn't fire. I couldn't assume anything, so for once I was forced to look properly: not for "eye," but for where the light stopped and the dark began. I covered the whole sheet in charcoal and erased the light back out of it, and it was, by some distance, the best drawing I had done. The tutor running the department asked me to draw his son next, which for an eighteen-year-old was roughly equivalent to being knighted. I didn't understand at the time why the worst seat in the room had produced the best work. It was years before I discovered the trick already had a name, psychologists call it the Thatcher effect, first demonstrated on a photograph of Margaret Thatcher with her eyes and mouth flipped, a change that's grotesque the moment the image is turned upright and almost invisible while it's upside-down. What it actually proves is that recognition and observation are not the same skill.

That's the trap a writer falls into with a script they've read fifty times. Recognition takes over. You stop seeing the page and start seeing the film you already know.

Here's a useful, slightly humiliating exercise. Explain the story out loud, what's powerful about it, what's funny, what breaks your heart, and record yourself doing it. Then go back to the script and find, line by line, where the audience is actually given each of those things. Where do we see it. Where do we hear it. What behaviour lets us infer it. If you find yourself needing to stand next to the page explaining what a scene really means, the scene has unfinished business, and no amount of your own conviction is going to finish it for you.

Autobiographical material makes this considerably worse, because real events arrive pre-loaded with meaning you didn't have to earn. You remember the room. You remember what happened six months later and what it turned out to mean. A stranger gets none of that. "But it actually happened" has never once been a defence anyone accepted for bad pacing, and reality, frankly, has terrible pacing. Films don't have that luxury, so real events sometimes need compressing, reordering, or merging three people into one, because the question worth asking eventually stops being "what happened" and becomes "what arrangement of what happened does the most damage to a stranger's composure."

Writers get sentimental about individual scenes too, in ways they'd never tolerate in anyone else's script. The scene took three days to write. The line is beautiful. It happened exactly like that. Everyone laughed at the table read. None of that buys the scene tenure. A scene spends screen time, and it has to earn the spend. Something should change: information, danger, status, desire, trust. If two characters leave knowing and wanting exactly what they did when they entered, the scene is probably stalling. Often there are twenty useful seconds buried inside four pages. Save the twenty seconds.

Reading the script aloud helps because weak dialogue becomes harder to disguise. Exposition announces itself. Characters start sharing the same syntax. If actors repeatedly stumble over a motivation or transition, inspect the page before blaming the performance.

“Write what you know” is useful only if you understand what knowledge is for. Experience gives you behavioural truth and specificity. It does not dictate subject matter. Someone who understands grief can put it inside a spaceship. The transformation is the writing.

Then try the test that comes, unhelpfully, near the end. Forget the pitch, the research, the explanation you give people at parties, the film that plays flawlessly behind your eyes.

Read only what you actually wrote.