Diversity saved my bacon :).
Little bit of adsense, little bit of SEO, little bit of direct ad sales, little bit of direct sales, all wrapped up makes for stable income. Even when one aspect has the bottom drop out of it. And in my niche I have 3 solid white hat sites that rank OK; one primary but if the primary ever dies I have 2 more ready to go with very little push.
One of the projects that my spouse accused me of "working on stuff that doesn't make any money" is making up almost half my monthly income right now.
(OTOH a couple of things my friends make very good cash on, I'm lucky if I get $100 a month on).
I'm building the structure for another website that's not even in my niche right now, not even sure how I'm going to monetize it 100%, but I think there's a reasonable chance it'll produce an ongoing revenue stream as well. Always good to have one more thing in your back pocket.