I don’t think most people really grasp what “install” actually means.
They’ll download an installer and often times, save it to their Desktop. They think that is the application and that the download was the install.
Even after opening the installer and clicking through whatever wizard steps there may be, the user often thinks that the installer itself is necessary to keep. Or worse, that they still must access the application from the installer.
You know these people when you see their Desktop is littered with a bajillion installers. Another giveway would be the AOL and other crapware icons left on the Desktop after buying the PC in the first place.
Couldn’t even guess at percentage. It’s way more frequent than I’m comfortable seeing.
Point is, such a person might tell you that yes, they know how to install software. Of course! But in reality – sad, sad reality – they definitely do not.