The fundamental theorem of PokerBots states:
"Don't try to play optimally. Try to play optimally against your opponents."
The game of poker is a people game. Different strategies are struggling against each other in a competition about money. When you are playing poker, forget about analysist watching your game from a TV perspective searching for weaknesses in your gameplay. They are not your opponents. Whoever is in the game is your opponent.
Playing poker optimally in general is not possible. Every strategy has weaknesses. Only optimal strategy against your current opponents can lead a player to success.
Two major concepts can be deducted from that approach
a) Find your opponents weaknesses and exploit them
b) Adapt your strategy so opponents cannot exploit your weaknesses
This is what experts mean when they tell you to change gears during a game.