Why sometimes over SPP in drilling make a dogleg, sometimes make a key seat?

Key seating is a major cause of mechanical pipe sticking. The mechanics of key seating involve wearing a small hole (groove) into the side of a full-gauge hole. This groove is caused by the drillstring rotation with side force acting on it. This condition is created either in doglegs or in undetected ledges near washouts. Generally, long bit runs can cause key seats, therefore, it is common practice to make wiper trips. Also, the use of stiffer BHAs tends to minimize severe dogleg occurrences. During tripping out of hole, a key-seat pipe-sticking problem is indicated when several stands of pipe have been pulled out, and then, the pipe is stuck.