I agree that his indolence and lack of hunger are exactly what prevent him to take "that" step.
Partially wasted talent and who knows if his attitude can improve, but well, potential is there (with an option to buy).
On a side note, about the extra spice to the derby... Ljajic was temporarily dropped off the Serbian National Team because he refused to sing the national anthem out of personal (religious) beliefs.
He's a "Slav Muslim from southern Serbia's ethnically mixed region of Sandzak bordering Bosnia and Montenegro"... probably enough said.
Especially if the coach who set the rules at the time and called Ljajic disrespectful was Mihailovic, a man who proudly paid a tribute to the Tiger of Arkan together with Lazio Fans.
I don't know if Ljajic is aware of all of this correlations...something that (ideally) should stay out of the field, but still, this is football and external implications are inevitable.