 My last piece of common wisdom was made famous by the Oracle of Omaha, Warren Buffett himself, which is to invest only in what you know. Now, when Buffett proclaimed this mantra, it was 30 years ago from an individual stock picker who was making large bets on single stocks. So yeah, that's logical to know those companies well, to comb through their financials before you put a big slice of the pie into one company.