At time's people limped in when the price is cheap to see the flop. Many books has emphasized on limping in with certain hands and raising with top hands {such as AA , KK,QQ,) And then when you see the flop you may have trips. Then when you reach to the river you lost to a better hand maybe a straight , quads to a royal flush. Either or you never know. Most players who wrote books have given there view. Then when you take their idea in the real world you get