Thevinins Theorem will show how a complex circuit can have a simple 2 resistor equivalent. If you remove the output resistor and measure the open circuit voltage of 32 volts. Short the voltage source and measure the resistance looking in from the open circuit output which is 8 ohms. Take the measured 32 volts and apply it to the voltage for the equivalent circuit. Take the measured 8 ohms and place in series with the original 8 ohm output resistor. You got the equivalent circuit. Shows you got the maximum power transfer to the output in the original circuit, since the series resistor and output are the same value on the equivalent circuit. Both have 16 Volts and 2 Amps.
