If you judge someone or if someone does something to you we tend to look only that event. We do not see the bigger picture. There must always been a preceding cause for someone to think or act in a certain way. If you consider that we're all in the same boat and all have to face existential problems (the questions I mentioned in your last question) then a sense of empathy arises. This perception needs to be put to the fore via sati (recollection or mindfulness) and with this recollection the perception gets stronger and stronger.

If you are condeming a person there must be a preceding cause for that to arise. Maybe you were angry which resulted in a negative state of mind, which further gets strengthend by indulging in more negative thoughts, or you are telling yourself that you shouldn't think or feel in a certain way because you are a spiritual person etc. Every state of mind (whether wholesome or unwholesome) **filters out** unfitting information. I hope this makes somewhat sense? Don't believe this, look for yourself next time you feel good or bad and how the subsequent thoughts will be. When you feel positive how is your outlook in regards to life?

To answer your second question: You don't need to do formal meditation to do this, it can always be done via recollection in daily life but in formal sitting it's most effective. You just consider the basic predicaments which every human has to go through. **Asking questions is more effective than just telling your mind certain "truths" , "teachings", "drawbacks". Whenever we pose a question our brain is forced to think (remember school?).** Just reflect on causes and conditions that weren't developed just now. Every human being has to cultivate skills/behaviours, emotions and mental states. Whether wholesome or unwholesome. If one was raised in a negative environment and had no insight into cause and effect etc he is not to be blamed because he is a fallible human. This is equanimity and compassion.