Just read a Motley Fool article titled: 4 Critical Errors You Must Avoid
which reminded me of another Fool article titled: How to Double Your Money
The lesson is the same. Basically, do not buy a company _just_ purely based on a peceived macroeconomic trend (aka hype). E.g. Nanotech is the next big thing, biotech is the next big thing, baby boomers are going to need lots of healthcare, etc.
What is more important, is the company-specific factors themselves, e.g. how competitive is the company, does it enjoy a monopoly? is its management good? etc.
The macro trend provides the "tailwind" that can push a stock further, provided the company is already speeding in the first place.