For many people, there is a clear distinction between what actually happened and what they wished would have happened in a given situation. Sometimes, people realize a number of options they could have or should have taken instead of the action they actually took. This feeling of regret or second-guessing is summed up in the expression woulda coulda shoulda. A man who handed over his wallet to a mugger, for example, might agonize over whether or not he would have been smarter to flee the scene, could have attacked the mugger, or should have refused to comply.
The expression is actually an informal rendering of three conditions: would have, could have, and should have. These are considered subjunctive moods, because they imply possible or theoretical conditions, otherwise known as wishful thinking. The mugging victim would have run away, could have attacked the mugger or should have drawn attention to himself, but none of these conditions actually happened.
"Woulda coulda shoulda" circumstances are more common than many people would like to admit. A nervous adolescent boy asking a girl for a date may get tongue-tied on the phone, but later realize what he might have asked her during the conversation. An employee explaining to his boss why an important project is still incomplete may offer up an ineffective response for why he didn't do it. For those seeking concrete answers, a "woulda coulda shoulda" reply can be translated as a defensive dodge.
Some people do not respond well to hypothetical or subjunctive reasoning, which is why they may use this phrase to express their disappointment or frustration. Any use of the words would've, could've, or should've in relation to a situation that appeared to require definitive action could easily trigger a derisive response. Sometimes, a better course of action or a more informed decision is only discovered after the fact, leading to a punishing round of conjecture.
Second-guessing a decision or exploring other possible responses after the fact is not always a bad idea, but it's possible to become so caught up in the paths not taken that a person can get caught in an endless cycle of "woulda coulda shoulda" blame assignment. Sometimes, it's best to make the best decision possible under the circumstances and leave the second-guessing and rehashing for another time.