Why writing a book takes so long: you're describing someone putting on a seatbelt and realise you don't know the words for the bit the metal bit goes in, or the name of the metal bit. You spend five minutes looking them up. It turns out one is the buckle, the other the tongue.

You spend another five minutes checking that you're right and it's not US terminology or UK terminology or some other kind of seatbelt mechanism that wouldn't be fitted in the car you specified more or less at random a couple of days ago.

You write the scene.
'Her hands were shaking so much she couldn't slide the tongue into the buckle.'
You realise few readers will know the words for the parts of a seatbelt – you didn't, after all – and this sentence is therefore meaningless and confusing.

You delete it. Your character sits in her seat, unable to fasten her seatbelt. You sit in your seat, unable to describe the act of fastening the seatbelt. The word 'tongue' looks increasingly strange. You think about drawing a diagram, or switching to writing film scripts.

You redraft the paragraph.
'She was shaking badly as she tried to fasten her seatbelt. Without taking my eyes off the road, I put my hand over hers and slotted the metal tongue into place.'
It's okay. It's not AMAZING. The reader will know what happened. You can fix it in edits.

It's a nice moment of your hero multitasking while under pressure. It fits with both of their characters that she is shaking and he is competent. Otherwise, it's nothing much - a stage direction, a break between dialogue. No reader will choose it as their favourite scene.

Half an hour has passed. You have written 31 words and learned all about seatbelts. Almost none of that is on the page. And it still bothers you enough that there's a good chance you'll go back and delete it when you read through the chapter again.

I always say this, but it's the mundane bits of life that are hardest to write and take the longest to get right.