Google SERPs are changing fast and very unpredictable. I used to get pissed off by Google as well. But thinking from Google's standpoint, it is understandable that they have to do what they do to outsmart those who try to manipulate the search result. However, over the last couple of years, I have found that Google does have its consistency as well. If you do the right thing and you will be rewarded tremendously by Google.