One thing I found confusing: When Cashier Wah is begging for Leung Jan to be his Sifu, Leung Jan firstly denies him, saying that to learn Kung Fu for the purpose of revenge is against it's principles. However, when they are training later in the film, there is a sign on the wall in the training room that says "Vengeance". Later on, Lueng Jan says that there is only one word to remember ("Vengeance"). So does he approve or disapprove of revenge?
shareTo my understanding, what he means is not to use it negatively, but to bear the word in mind to keep the focus of it. Like it's not to be used carelessly, but if you are called upon to use it, be aggressive and ruthless and do what it takes to protect yourself. Wing chun is a very aggressive system designed to overwhelm the opponent, hence the close range fighting, not many people are used to having someone come at them like that. To think of vengeance keeps you focused on taking the other person out.
Like a lot of martial arts, you have to be responsible with your skills, but ultimately, if someone does force you to use it, put them down.
Hope that makes it a bit clearer for you.
Kung fu movies are like porn. There's 1 on 1, then 2 on 1, then a group scene...