From the Darth Plagueis novel:Leia was walking around Vader and he didn't know it was his own daughter (of course retroactively once RotJ turned her into Luke's sister).
The movies have set up, and now canonized, that you can close yourself off from the force. So Palpatine was just a typical senator.
In concealing yourself, you will not be able to rely on your dark gifts, Plagueis said. Instead you must be yourself, submerged in the unified pattern to which the Jedi are attuned; visible in the Force, but not as a Sith. Since you cannot allow yourself to be seen, you must make certain that you are taken for granted. Disguised in the profane; camouflaged in the routine—in those same realms from which you can attack without warning when necessary.
We Sith are an unseen opposition, Tenebrous had told his young apprentice. A phantom menace. Where the Sith once wore armor, we now wear cloaks. But the Force works through us all the more powerfully in our invisibility. For the present, the more covert we remain, the more influence we can have. Our revenge will be achieved not through subjugation but by contagion.