I feel like Hourglass is a song about how we often regret the decisions we've made in the past. This can either be words we've said, the time we've wasted, or the decisions that still hinder us in the present. The protagonist is angry at themselves for the mistakes they have made, so they actively punish themselves for their old choices. This causes them to dwell on their past decisions, which doesn't allow them to truly live in the present. The stress of the choices they've made in the past causes them to spend more time hating themselves, and they don't get to truly experience their present. For anyone who may need this, don't dwell in your past. All you'll do is waste time that you could be using to improve your present and future. Don't look back, unless there's something you need to find.