Often, people who want to start a business will ask my advice. For instance, if they are thinking about starting an online business, they will ask if they should have a blog. Sell advertising on their site? Create an ebook? Sell physical products? Offer services? Promote affiliate programs? My answer: Yes. Do all of those things, or as many as you can manage.
While they are often looking for one thing they should do, I believe that you should have many ways of generating income. The same is true for offline business. If all of your revenues come from one source, what happens if that revenue stream dries up? That can happen if you do not diversify your business.
Diversification can come in many forms. For example, you might do business both online and offline. Many small retailers have found that having an online business allowed them to keep their businesses afloat, and even expand, when their brick and mortar stores went through tough times. And for some, having the online business meant they still had income, even if the store did not survive.
Some online businesses have gone the opposite direction, from being Internet-only to opening physical locations to serve customers locally.