Keyword research do not depend on your assumptions alone
Proper and extensive keyword research is the first and most crucial step towards building a search engine friendly website. However, a lot of new and tuned webmasters tend to depend on their own assumptions to determine related keywords. Perhaps they forget that they are not the intended buyers.
Where is the loophole?
The problem is there in the core keyword research process. And when you are using a free keyword research tool, it does not allow you enough options to fine tune your search. The results provided by these tools mostly depend on your own assumptions.
An example may demonstrate the process in a better way.
Say, you are searching keywords for a website that sells MP3 music players. Inevitably, your research will start from MP3 music players which will provide you some keywords like:
100% free music downloads for mp3 players, concepts music express mp3 players, download music video for mp3 players, free downloadable music for mp3 players, free music download for mp3 players, free music downloads for mp3 players, free music for mp3 players, free music uploads to mp3...