A good research project usually involves using multiple sources and different kinds of information.

A common mistake students make when writing papers is to rely on one or two sources and to only use one type of source.

Number of Sources:
If you rely on one or two sources, you probably are not going to get very complete coverage.

Different Types of Sources:

If you only use one type of source-only magazines or only web sites, for example--you'll probably miss lots of useful information