A patient arrives at your office with their full gold crown in hand. They explain to you that another dentist delivered it last week. You then examine the crown and the preparation. What is the most likely reason for dislodgment of the crown?
Retention form depends on:

Minimal amount of taper (2 degrees per wall) on the vertical walls of the preparation.
Length of walls.  
Circumference.

The most common cause of failure of resistance form can be due to increased taper of the prepared tooth. Optimum values of taper is 6° with a minimum of 0°-2°.
In given case, the preparation height is adequate (4 mm) and since the crown did not dislodge immediately, it shows to have adequate luting cement.
Jagged and undefined margins increase susceptibility to microleakage and their role in failure of resistance form is minimal.
There was very little cement in the crown
The preparation was only 4 mm high
The preparation walls were tapered at about 15°
The margins were jagged and undefined