Don't go into monopoly markets; there's no chance.

Monopoly markets dominated by a few major players severely limit your options.
Markets where years of relentless competition have produced numerous underdogs are dangerous.
Even fully competitive markets offer little hope, as you cannot compete against established giants.

These markets are typically filled with very similar competitors, battling over prices and minor differences. This saturation makes it difficult to enter such markets, and even existing businesses within them struggle.