I'm in a basic circuit analysis class. I'm having difficulty consistently calculating Thevenin's equivalent resistance. I've been operating under the assumption that to find this value, you simply replace the load with a break, short the voltage sources, break the current sources and calculate the resistance...

However, working some example problems, it seems that gives an incorrect value. Rather, sometimes, to find the equivalent resistance you need to find current through the shorted load and the voltage across the open load... Then of course R=V/I.

It seems from looking over examples I have, the correlation on when to use which method involves having dependent sources. Is this correct? If so, why is this the case?