Sri Krishna advised Arjuna to fight with heart in the battle against Bheesma especially. But Arjuna was fighting half heartly which could make Pandavas lost the righteous war against Kauravas.
The Battle of Maharbharat is about the war between the evil and truth.
Even if ones own persons are taking the wrong side, one should stand against them .. Is it easy to follow today ? Not doing battle in today's time of course.
But raise the voice or refuse to be part of activity against right persons.
Everytime Arjuna did not fought war properly against Bheesma.
Shree Krishna advised him many times. Then he himself took chariot wheel since he had promised not to take part in the war or use weapons. Just do the role of charioter .
On seeing Shree Krishna coming with the wheel towards Bhisma, Bhisma came forward to greet him knowing he is a god and he would be liberated after meeting death from the hands of god.