Even when the power supply was connected to the ESP8266, it would not boot properly.
After some research, I found an article on how to stabilize the operation of the ESP8266.
However, it seems that when the ESP8266 is powered on, it must go HI in the order of "power supply -> EN pin", and to make it so, it is necessary to connect a resistor and a capacitor to the EN pin to delay the EN HI to be delayed from the power supply.
I actually did it and it no longer fails to boot!
The ESP8266 circuit based on the above is shown below.
