Normal construction techniques do not typically ensure that your door jambs are solidly mounted to a stud in the wall.  There can be a gap between the jamb and the stud of 1” or more and this effectively weakens your security. 

It is possible to push the jamb in the center where the lock engages the strike to a point where it will flex beyond the 1” throw on a deadbolt.  Once that happens, just touch the door and push it open.

The way to prevent that is to place some reinforcement between the jamb and that stud right at the center of the jamb height.  Jamb construction dictates that only the inside trim should be able to be removed, so remove that trim.  That will expose the amount of space between the jamb and the stud on each side.  What you need now are called shims.  You will need at least two for each side.  Shims are wedge shaped and you can see that if they are moved against each other the effect is to make them thicker.  That is how we will fill the space.  Shims can be obtained ready-made from your favorite lumber supplier.

Place the shims in position and then drive them against each other until they are tightly wedged in place.  Then place one nail or screw through the jamb, the shims and into the stud to hold them in place.  Your jamb is now as strong as the double stud used to frame the opening.  Replace the trim and you are finished.