There is a counterfeit of discernment that is really just a critical spirit wearing a halo. Jesus warned about it in the verses just before this one. People take a fault finding heart, baptize it, and call it discernment. They say they have discernment, but notice that everything they discern is negative. This person cannot be trusted. That person is horrible. That is not wisdom. That is a plank.
Real discernment, is the ability to tell the difference between a struggling brother and a scornful enemy, between a child who is rebelling and a child who is simply suffering. A good parent is neither harsh nor blind. The harsh parent pounces on every mistake. The blind parent sees nothing. The wise parent knows the child. That kind of knowing love is what Jesus is calling out of you.
So test yourself honestly. When your discernment speaks, where does it lead you? If it always leads to suspicion and superiority, look in the mirror, because there may be a log sticking out of your eye. True discernment is just as likely to lead you toward mercy as away from danger.