Adsense Earnings Stagnates

My adsense earnings have been stagnating for the longest time. For the past half a year or so, there has neither been a decrease or increase in my earnings.

Interestingly, some sites which I have not bothered updating are actually the ones that are giving me the regular stream of income. While others which I have been updating frequently are not as "productive". Perhaps the strategy I am using is wrong.

There is one particular site that I own which apparently gets the same number of visitors for the past 3 months even though I have not updated it at all!

After all, I have heard people talk about being passionate in what you do. And I guess that motivated me to throw away all the keyword research and SEO that I have been doing in the past. All the keyword research and SEO that I did in the past are probably what got me to where I am today.

I think I need to work smarter to make my adsense earnings go up.