I have a more sensitive sniffer than any of the people I live with. I smell things long before they catch on. This is sometimes a good thing--I catch the dirty catbox before my roommate says it stinks.
But sometimes it's a bad thing; my SO doesn't catch on to the fact that the trash needs to be taken out before I do.
I thought I was smelling a phantom smell of smoke at a client's house until I realized what I was smelling was a downdraft through the chimney and fireplace, which they hadn't swept out in a while. That was a relief.