The TAB key is a very important tool! Everyone will tell you so...but not everyone latches on to its use right away either.
For example, you want to select all the exterior walls, you just hover your cursor over one wall, press tab (once, don't hold it down or else you get "disco tabbing"), then click (yes the left button). All selected!
Users are prone to move their cursor away from the element they are hovering over which causes Revit to lose the highlighting they carefully TABBED to acquire. They also get confused about whether they should use the Right Click or Left Click, yes use Left Click.
Definitely truly a quirky Reviteristic.