Actually, they didn’t so much lose it, as delay. Then they proceded to make mistake after mistake in trying to get it back to us.
We left Rochester, NY, flew through Cincinnati to Seattle. Our single bag didn’t arrivw with us. Apparently it went to Detroit, to Salt Lake City to Seattle or something like that. We arrived a little after noon. Our bage wasn’t due until sometime after 4pm. But we were staying in Kingston  across the Puget Sound. They said they would deliver it that night, in the morning. It didn’t arrive. According to Delta Airlines website, our luggage should have been delivered between 6pm, and 6am. I called Delta Airlines. They said our luggage was now going to be delivered before 6pm. But I called the courier and found they didn’t even deliver  to Kingston. They were waiting for Delta to tell them what to do with it. Delta Airline seemed to think they delivered to Kingston. After hours of phone calls, and incompetence by Delta Airlines. We finally drove 80 miles round trip to pick up our bag in Por Orchard. The other option Delta gave us was to have the courier deliver the bag back to the airport, and they would fedex  the bag to us. But then we would have to wait another 2 days to get it. Still not happy about the whole situation.
I have had more problems with Delta Airlines than all other airlines combined.