I'll give you my own experience. I know telecommunications, since I come from that professional background. I know how the business works, and although I am not an engineer I do have some facility in understanding how components work and how the companies providing them derive profits. I believe these are the best in their fields, and I am convinced that I know why. But telecom has dropped as of late, as have my holdings listed above.
Diversification is a good thing, in and of itself.
The theory is that companies in various industries are beholden by different economics, so when the PC industry has a downturn, the banking industry is not effected. But lately diversification has seemed to take on two less tenable meanings. Here's the thing, and I mean this in the best spirit. Either they don't think you are very smart, or they themselves know less than they think about commerce. But a fair number of the technology companies are in fact going to wither up and fail.