There are a variety of reasons that we may be happy at the exact same moment when someone else is in pain or failing. In the case of this teaching from the Talmud, the angels cheering on the Israelites were happy to see the slavemasters and charioteers of the Egyptian Pharoah drowning in the Sea of Reeds. The failure of the Egyptian army meant the survival of Israelite families. In this new (secular) year let us not rejoice at the downfall of others, but rather let's weep that suffering exists for anyone.