No matter if you're doing blackhat or whitehat, online or offline, it's always best to distribute your wealth. Putting your money and work into one company, one bank, one stock, one website, one search engine, one method, etc. - that adds up to too much risk.
There are so many factors affecting each of those things that it's a suicide mission to rely on only one source or method. What if you lose SERP? What if you a new competitor beats you? What if a company you rely on fails? There are too many random variables.
However, if you are new, I do suggest you maybe focus on one method at a time. Find out what works best for you rather than just diving in and trying everything. Once you figure out what works, you can distribute your one method across multiple sources of income (i.e. different sites, different niches, etc.).
Once you master that method, you can master a different method and again spread it out across various revenue streams. You can see how that multiplies into many, many "baskets."
For example, I have a couple offline companies, a few online sites, a traditional job, and other various means of income. If I get banned from a CPA (which has happened), drop in SERPS (which has happened), lose clients (which has happened), I'll be okay because there are other ways I can get money.