But for is used to introduce the reason why something didn’t happen.

But for the traffic jam, I would have come in time.

Если бы не пробка на дороге, я бы пришел во время.

(The traffic was very heavy. If it weren’t for the traffic, I’d have come in time.)

Схема составления предложения, используя оборот But for…

Examples:

They would have all perished, but for the quick thinking of the driver. (=… if it hadn’t been for the quick thinking of the driver)

But for the flight cancellation, I could have arrived at the conference.

Task:

Make up your own sentence or describe a real situation using but for …