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Considering that you have a finite amount of time, passive income should make up a large part of your work. And if you're serious about generating any semblance of income online, then passive income should be one of your sole goals and ambitions. Why? Simply this. Wouldn't you prefer to do the work one time and get paid repeatedly as opposed to relying on your time to generate that income?
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.