Question: > 
> Many an opportunity is lost because a man is out looking for four-leaf
>  clovers.
> 
> 
> 

I have no idea what the quotation means. Is there any special meaning about four-leaf clovers that I may be unaware of?

Answer: 
The only reference I can find right now says that the ratio of three-leaf to four-leaf clovers is ~10,000 to 1. I would interpret that saying as meaning that you're likely to miss real opportunities if you spend (waste) your time looking for a rare item to bring you good luck.
It means valuable opportunities are easily squandered by spending too much time searching for things that are difficult (or impossible) to find. 

For example, chasing after a scholarship from NC State with single-minded intensity may cause someone to miss the fact that they've been already been accepted by ECU.

IDK if that helped; I hope it did. :)