Being a non native speaker of English I am not sure about the usage of had. In my academics I have learned that had is only used to show that something happened prior to some event in the past according to rule of past perfect. Like we do say
When we reached the station, the train had left the station.
But now-days I see usage of had to show some past events irrespective of any prior event. Like I have listen
What had made you so tensed?
According to my teacher this sentence is wrong as there is no prior event associated with it.
Could anyone clear my confusion about over all possible correct usage of had used in past events?