Its hard to not be so negative because that's the way we've been taught to respect the negativity. I say that we only do that when it helps, and draw the line when it becomes just pure emotion and useless. Think about how much more enjoyable your life would be if you laughed and learn from accidentally spending 100$ on something that you don't even need. I don't think in that situation in any way that it would help to be mad and disappointed at yourself. Just disregard it and move on.