Sentence examples for but lost from inspiring English sources

"but lost" is correct and usable in written English.
It is a conjunction and can be used to connect two clauses or ideas that contrast with each other. Examples: 1. I studied hard for the test, but lost my focus during the actual exam. 2. The team played well in the first half, but lost their momentum in the second half. 3. She wanted to buy the dress, but lost interest when she saw the price tag. 4. We planned to have a picnic, but lost our enthusiasm when the weather turned bad. 5. He thought he had everything under control, but lost his cool when things didn't go as planned.