One of the bad features of AdSense blinders (having Google completely separate you from the task of getting either readers or advertisers) is this familiar fallacy:
If one page makes me $1/day, then all I have to do is come up with 999 more pages, and I'll be making $365,000/year!
Why does this reasoning virtually always diverge so far from reality as to be useless?
Good ol' Zipf For any website with a non-trivial number of pages, you invariably end up with a Zipf distribution of traffic (and earnings!) across your pages, which is about as far from a uniform distribution as you can get. 20% of your pages will get you about 80% of your earnings, so you end up "wasting" (assuming we ignore secondary effects) 80% of your time. Wasting 80% of the time you spent creating 10 pages is a very different feeling than wasting 80% of the time you spent creating 1,000 pages. It may become difficult to stay motivated!
Look at this another way. You have to write 10 pages to get 2 that perform significantly better than your average (keep in mind, your "average" will quite likely be closer to $.05/click than to $1/click). To get 20 good performers, figure on writing 100 pages. To get 200 good performers, yup, you need 1,000 pages. Will you really have the energy to shoot for 2,000 good performers? (Of course, this is a general rule and a general law of distribution -- please don't bother to post how your specific numbers are woohoo better or boohoo worse. The point is, if you're starting out and you believe your website is going to magically be immune to the curse of the Zipf distribution... well, I guess you can always give Amway another try after AdSense doesn't work out :-)
You can't predict. You'll see people in this forum poring over the Overture bid tool or the AdWords SWAG tool to find the keyword X that will make them $2/click. Only to discover that keyword X actually pays you only $.05/click, while keyword Y, which you failed to really develop enough content on, is paying you $1.50/click (even though it was a keyword you never even thought to research, let alone really target).
Things change. You'll see people yelling at Google for "ruining their business" here. For many of them, they got pretty much flat-out lucky and ranked highly for some high-paying keywords. Unfortunately, they attributed their success to just being really smart, so instead of continuing to buttress their content and spread their risk out, they just sat on it and got destroyed by the next big Google algorithm update. IOW, they had a lousy Google Stability Number [webmasterworld.com] and did nothing about it. Because things change, you have to budget for maintenance (or watch your SERPs slowly slide into oblivion as competitors smell money and put the work in to top you), and maintenance probably grows in proportion to the number of pages you have, which will surely slow down any amazing ability you have to grind out new pages at high speed.
Traffic has limits Hey, look at me making $1/day off my Miami Musings. Hey, look at me making $2/day after I double my Miami Musings page count. Hey, how come I'm still only making $2/day even after I wrote 10 times as many Miami Musings pages? Ooops, guess there was a limit on how many people wanted to read about that.
Ad inventory has limits Hey, look at me making $1/day off my Miami Musings. Hey, look at me making $2/day after I double my Miami Musings page count. Hey, how come I'm still only making $2/day even after I wrote 10 times as many Miami Musings pages? Ooops, turns out most of my money was coming from one advertiser, and his AdWords budget was set to $2/day.
Self-competition Man, my Miami Musings post about the new "Miami Vice" movie is so popular, I'll create some more content on that topic. Ooops, now the traffic/clicks I was getting on that one page are effectively spread across my now multiple pages on the topic, with only a small net increase in either traffic or money. In my mania to grind out new pages on my favorite topic as fast as I could, I just ended up competing with myself.
High velocity means lousy control As alluded to in the previous point, an ability to spit out lots of pages real fast goes right along with an inability to realize you're headed down the wrong path before you've wasted too much time. Slower content creation (which sometimes goes along with better quality content) makes it more likely you'll see that Topic X offers lousy returns before you've written 30 pages on Topic X. Also makes it more likely you'll see that you can dominate the SERPs for Topic X with just a couple of pages, so you don't waste time writing 28 more pages that essentially just cannibalize the same traffic across more pages.
On the plus side, it couldn't be easier to just take a whack at any content topic under the sun, slap AdSense on it, and see what happens. That's good, because that's just about the only way to find out how much (or little) money you can make. If you're making $20/day off your nice little 20 pages of content, and you think that means you can just add 20 more pages and make $40/day, then you're probably in for a rude surprise.