Only clear recollection from the book is an example along the lines of:
Experience: I know I put my keys on the table next to the door, but when I went back they weren't there. Looked all around the house, happened to pass by that table again - and there they were.
Reason: the person had slipped into a near-identical parallel-ity in which the keys had not been left on the table, and then slipped back again into the previous reality - or at least into another one which had the keys on the table.
Perhaps a person or a team became aware of this, and some story took off from there.
Almost certainly 1985-2005-ish. English. Read in USA. Probably a stand-alone novel. Almost certainly more sci-fi than fantasy. Thought it sounded like a James P Hogan, but couldn't find one like it among the paperbacks at hand here. And - at least with the search terms tried - couldn't find a match by a web search.