Although best known for his macro-economic insights, John Maynard Keynes was one of the first and most effective fund managers in history. For more than two decades he oversaw the endowment of King's College, Cambridge, resulting in a tenfold increase in capital. He summarised his strategy as follows:
"The right method in investment is to put fairly large sums into enterprises which one thinks one knows something about and in the management of which one thoroughly believes.
"It is a mistake to think that one limits one's risk by spreading too much between enterprises about which one knows little."
It is possible Keynes also benefited from what today would be considered insider-trading, but might also have simply been diligent research. Still, the key lesson was that he invested capital intensely into what he knew.
His modern-day equivalent, Warren Buffett, also prides himself in shunning investments in things he does not understand; famously avoiding the internet boom and resulting tech wreck. For those who understand the digital age, avoiding technology would make little sense but for Buffett, who did not, avoiding it was sensible.
We all possess some degree of inside knowledge, areas of expertise that are unique to us. Making use of your own insights, contacts and understanding is more rational than taking a punt (or alternatively not doing so) on an investment because of something you read in the paper.
Invest in what you know and understand. Anything else is gambling.