Very few homes have locks that were properly installed to begin with.  In new construction, the outside doors come prehung in a frame from the factory and are installed together as a single unit.  One contractor usually installs these door/frame units and another contractor installs all hardware (locks included) throughout the house or apartment.

    The door installer is usually a general carpenter that installs the door/frame units using nails in the door jamb.  Once the frame is secured, a fastener that holds the door closed in the frame is removed and the door is checked for ease of opening and closing.  Here the door installer's job is completed.

    The hardware installer has contracted to install all hardware in proper position and working order.  This is where the ball gets dropped causing the problems you are probably having right now.  Most of these door/frame units have one or two screws missing in each hinge.  The hardware installer is supposed to use long (three inches or longer) screws to secure the frames to the 2x4 studs in the wall.  That is because outside doors are thicker and usually solid and thus are much heavier than regular inside doors.  As time goes on, the weight of the door will cause the frame to give and let the door sag.  This is when you start having problems like the deadbolt being hard to turn, the door knob not keeping the door shut or the door dragging and being very hard to open or close.

    Another oversight is the hole in the frame for the deadbolt latch.  I have never seen a frame from the factory that has had the hole cut out deep enough.  The factory mortices the hole in the frame for the deadbolt to the same depth as the one for the doorknob.  All modern deadbolts have a one inch throw and do not deadlock into place until the latch extends to the full one inch length.  An easy way to tell if the hole is deep enough is that the hole will go all the way through the frame.  The wood used in the door frame is less than one inch thick.