edit:Yeah, now I got it.
If we apply KVL:
VBE = 3V - 0.7V - (R1 * IB)
Let me ask that sometimes instead of a diode, they draw an external resistor which is called (pi-resistor) instead of the diode.
At this specific point I got confused. I just aren't we gonna use diode everytime? Therefore, when should I have to put pi-resistor inside the model?
As an exemplifying here is a representation of pi-resistor.
It seems that they did not use any diode inside it. That is why I just got confused, sorry for that.
Actually, this is just an example image for the pi-resistor that I found randomly.
I just wanted to say that, until now I have been always putting a diode, but I really could not understand that why some people prefer the pi-model and instead of using a diode?