Sigh. Casting is hard. I look forward to the day when I can leave it all up to casting directors. Telling an actor they got a role they really wanted is wonderful, to hear their excitement (which they often try to suppress so as to sound professional) and to know you have brought them joy is always the best part of the job. Telling an actor that they got a role other than the one they hoped for is the hardest. I often have to put very talented actors in roles other than the leads for a variety of reasons, including that the smaller roles need good actors too.
I've been there as an actor. I know how heartbreaking it is to be passed over for the role you really want. I just have to concentrate on what is best for the cast as a whole and enjoy the happy phone calls as much as I can.