People have risen up out of some very tough situations to be successful...but it is not easy.
The word "investor" also could be part of the problem. This has been argued many times on BP, so for the sake of this thread I will assume investing means all forms of real estate investing discussed on BP (wholesaling, rehabbing, holding property, etc).
As Jeff was alluding to, there are many factors involved, money being one of them, although an important one. You do not necessarily have to have money, but you need access to it, whether through banks, lenders, private loans, investors, etc. Without cash, or access to it, it is hard to invest in anything. People often point to wholesaling as the method of choice for people low on starting capital. Wholesaling though is very difficult and requires and understand of real estate basics, property analysis, marketing, etc. If you do not understand those things, you cannot be a successful wholesaler.
Basically, I am trying to say it is not impossible, but will be very difficult and will require a lot of work, a plan of action, and some real estate knowedge.