To what extent is a surprise good?

When two parties are fighting against each other, there are some underlying rules between the two parties and both parties are following the rules to fight against each other. Sometimes these rules are unspoken rules which are not made public or written down. For example, during the Cold War, the usage of nuclear weapons was an unspoken rule and the two superpowers (the USSR and the US) not fighting directly on combats was an unspoken rule. However, sometimes one party might want to win some advantages by playing some surprising strategies, and often the first that comes to one's mind is to break the unspoken rules. Because the rules are unspoken, the parties do not take as much blame as they do if they break a rule that is known to the public. 

However, breaking an unspoken rule can have very serious impacts on both parties, as it fundamentally changes the system of the game since the rule is changed. Once one party breaks an unspoken rule, then either party becomes unconstrained to all the unspoken rules, as the party which breaks a rule is likely to break more, and the other which suffers the consequence of breaking the unspoken rule then is also likely to take a revengenous action and break unspoken rules. Under such circumstance, the unspoken rules become invalid and the two parties continue the game without any constrain to the unspoken rules. 

Moreover, breaking an unspoken rule can be seen as a 'cheat' in a dynamic game, and the best response to a cheat play is to cheat as well. Therefore, the players in such design theoretically will always break unspoken rules and continue this manner. So it is fair to conclude that playing a surprise (to break an unspoken rule) is not really a wise strategy when cheat creates an outcome that only one party benefits and cooperation makes both parties mutually benefit but just a bit less and fight makes both parties gain much less (or suffer losses).