It would be a much happier place and things would still get done by driven, positive people.

I disagree with you that it's always the start of positive changes. Plenty of things can already be positive and you can still improve them without being disappointed in them, just reaching for a higher standard because you know you can do better. Certainly it can be the start of some changes, but I think that the attitude of always being disappointed would be unhealthy because disappointment is, as your title puts it, negative.

Many times I make changes because I need a new change of scenery or I just want something to just be different.