It's good to let out the truth when it's important.
Walt was walking down the road when he saw a robbery going on, and an officer asked him about it.
Walt has to decide whether to snith.
Walt tells the officer everything he knows about what he saw.
Walt told the officer that he didn't see any robbery going on.
The robber has a higher chance of being caught, and Walt feels like he's helping.
The robber gets to continue to cause harm, and Walt has to deal with the guilt.