I Could Have Done That

The worst phrase in art (or indeed in life) is 'I could have done that!'. The irony of such an utterance is that the speaker is instantly proving that they could not. People who can do things just do them, not tell anyone that they could if they 'wanted', if they 'tried'. It's a retort of envy. The positive thing to do is to prove you can do something by doing it, and doing it better.