A better question to ask is, "Why are developers grumpy?"
What bothered me most about this essay was one point near the end: "Ask yourself, 'Am I being grumpy right now?'. If the answer is yes, then stop!"
This is a non-realistic response to an issue of moral with a real underlying cause. What bothers me most about this is that it will only cause further issues with the developer as they cover the problems with the group they are working with. Their proposed solution is what someone would say to someone suffering from depression, 'Just stop being unhappy and cheer up!'.
This does not work, what they suggest will not work and will only further the decline of morale, company culture, and retention of developers. Grumpiness is a symptom of underlying causes within a company.