BP is also very subjective to circumstances:
-why do they always take your BP the minute you walk into the exam room? ANY exercise will increase your BP
-a sudden startle will increase your BP in a nanosecond (fight/flight)
-not feeling well? In pain or discomfort? Your BP will be elevated.
-Mad/frustrated from rush hour traffic/running late to appt? Just pissed off/having a bad day? = elevated BP
DRs just want to write Rx's for patients.