One least touted ill effect of stress or excess of it is the fact that it clouds your judgement. You want to just get through the moment and your mind being so stressed, cannot evaluate the options as well as it would do, say, when you were happy.The result is a wrong call. One wrong call can put you on the path away from happiness. With one mis-step and continued stress, you can make take more mis-steps and get farther and farther away from the fork point on the road to happiness. This reminds me of the path Anakin takes in the Star Wars movies (and of course, many living examples) – a perfectly healthy and happy young man lets anger be his source of stress. As the anger develops, he gets farther and farther away from good judgement and ends up being Darth Vader.