In the game of chess, there are (on average) about 35 moves a player can make. If we were going to have a player consider those potential moves and the 35 moves an opponent might make in response to those moves, the player would have to consider about 1,225 board positions:
35x35 = 1,225
If this same player were to consider the 35 moves he or she could make, plus the 35 moves an opponent might make in response to those moves, and then the 35 moves he or she might make in response to this opponent, the player would have to consider 42,875 board positions:
35x35x35 = 42,875
In 1997, Deep Blue could process about 200,000,000 board positions given the time it had to make its move against Kasparov or 5 moves which would equate to 35x35x35x35x35. This is called the brute force method where the computer's processing power determines how powerful its decision-making processing is.
However, when human beings like Kasparov play chess they definitely do not consider millions or even thousands of moves because we do not use the brute force method to make decisions. Instead, human beings use intuition and feel based on past experience and learning to make these decisions. We use larger strategies tied to experience, some of which have little to do with chess, in making our determinations.