Answer by Steve Denton:
In life, just as in chess, it can be dangerous to assume that other people always act rationally, and always have a carefully thought-out strategy that makes sense, and that you can anticipate and plan for their every possible action.
Experienced chess players can sometimes make the mistake of over-estimating their opponent's abilities in strategic thinking and situational analysis. As a consequence, they might assume that their opponent will share their own assessment of the possible rational options – which will most likely be smaller in number than that of the possible irrational options – and will choose the same option that they would if their positions were reversed. They will therefore have planned their next move based on that assumption. Because of this, they can sometimes be completely wrong-footed by a less-experienced opponent who has not performed a detailed analysis of the state-of-play, does not have a coherent strategy, and who simply makes an impulsive, random or even irrational move.
Faced with this surprising and apparently inexplicable move by their opponent, the more experienced player might suddenly begin to doubt their own analysis of the situtation and, still over-estimating their opponent, conclude that they have missed something, perhaps because they weren't thinking a sufficient number of moves ahead. They might then try to think more moves ahead, to the point where the number of possibilities overwhelms them and they can no longer formulate a coherent strategy. In the worst case, they might actually lose the game because of this, and to an inferior player who wasn't even bothering to give the game that much thought!
Of course, there is also the opposite error (again, in real life as in chess); that of under-estimating your opponent. If an opponent makes an unexpected move, which appears to make no tactical or strategic sense, an experienced play might mistakenly conclude that their opponent just made a dumb move, and is therefore probably an inferior player. But the truth might be that their opponent is actually a more skillful player and really is thinking more moves ahead and employing a more sophisticated strategy – which will ultimately prove victorious.
The moral of this is that, in real life as in chess, it is important to know your opponent's abilities, and to neither under-estimate nor over-estimate them.
Another important lesson that chess can teach us about real life is the disproportionate and nonlinear nature of the long-term consequences of apparently insignificant actions. Moving a weak piece, such as a pawn, a single square in an early stage in a chess game can have huge consequences in the climactic end-game, and can make the difference between victory and defeat. And the moral here is obvious; pay attention to the small details, and treat everything as potentially significant in the long-term. Following the development of the science of Chaos Theory, this concept has now achieved general public awareness via the catch-phrase 'The Butterfly Effect', which succinctly encapsulates the exponentially multiplying effects of apparently trivial causes.