Top 10 Reasons You Can't See an Element in Revit

1. Is the correct Workset being used?
2. Is the view range set correctly to see the particular element?
3. Is the object hosted on an incorrect surface like a floor instead of a ceiling?
4. Is there a filter applied to the view that is causing the element to be hidden?
5. Is the detail level of the view set correctly?  Some families are set not to show at Coarse.
6. Try using the "Reveal Hidden Elements" tool in the view control bar.
7. Is there a plan region in the view?
8. Is the view "Discipline" set correctly?
9. Is the element in the correct phase and is an appropriate phase filter set in the view to make it visible. 
10. Is the element part of a design option and perhaps that isn't the current option for that particular view?