…is to wish and pray for God’s mercy on themselves while at the same time wishing and praying for God’s justice on others.
Because if you are doing that it means you are forgetting this key line from the Our Father/The Lord’s Prayer.
Forgive us our trespasses as we forgive those who trespass against us.
I suspect that no line in general prayer is more consistently ignored by those pray it than this is.
Da Techguy's (no longer backup) Blog 
Indeed, it is one of the most dangerous things we can ask.