The road to hell is paved with good intentions

Meaning: 1) People who believe they are doing good can end up doing bad (the law of unintended consequences). 2) There is no value in simply planning to do good if you don't actually do it.

Note: hell (noun) = (according to various religions) a place of suffering where bad people go after death | paved with = covered with; constructed with; made of | intention (noun) = a plan; an aim

Origin: This proverb may have its roots in a statement in French by St Bernard of Clairvaux (c.1150): "L'enfer est plein de bonnes volontés ou désirs." ("Hell is full of good intentions or desires.")