Monopoly markets with just a few big players will severely limit your options.
Markets where years of ruthless competition have created a large number of bottom feeders are hazardous.
充分竞争的市场也没戏,你打不过那些老家伙
usually are full of very similar competitors, fighting it out over price and marginal differences. This saturation makes it hard to enter a market, and even the businesses that are already in that market suffer.