I wouldn’t be so sure.
One of my favourite things about making money from contextual advertising programmes (like adsense) is that you can give a pretty accurate guess at how much money you would be making with X amount of traffic. You just have the use the eCPM that adsense generates and x that by X amount of traffic.
Lets say that you have an eCPM of $1.00. (this is quite a reasonable amount IMO, I usually get a eCPM closer to $2.00)
Lets say you get 50,000 page impressions per day. (this is obviously quite a lot, but by no means inpossible.)
You would be making $50 a day straight up.
That’s $1,500 a month from just adsense. (not to mention affiliate sales, website sales etc.)
Now lets say you plug that money back into the site.
This month you get 100,000 page impressions per day.
$100 a day.
$3000 a month.
Repeat this process a few times.
Now do the same thing with 10 other website.
Obviously these figures are very rough, and are maybe slightly unrealistic… but you get the basic idea.
I like to aim high and be optimistic.