Continuity mistake: When Porter is tied to the chair being beaten up he is wearing boots and his legs are not tied to the chair. In the next few scenes when Mr. Bronson shows up with his hammer, now Porter has no boots on his feet and his legs are tied to the chair. (01:26:15 - 01:27:30)
Continuity mistake: When the Asian gang hits Porter with their car, the stunt double partially slides off the windshield. When it cuts, Porter is still lying on the windshield. (00:47:15)
Continuity mistake: When Porter and Val are about to Ram the car in the heist, one shot of the chinese car shows it without a grill, then the next shot shows it with a grill. (01:14:25)
Continuity mistake: When Porter goes to see Carter in his office to get his money, porter throws a roll of coins at Carter that he used to punch out the two body guards. Carter takes the roll and rolls it on his desk towards Porter. The very next couple scenes, the roll of coins is missing from the desk. (01:06:20)
Continuity mistake: When Porter drives the syringe into the wall at his wife's apartment, the wedding ring on it appears to go from on the needle, to the middle of the tube. (00:11:40)
Other mistake: When they crash head on into the gang's car before robbing them, in the brief shot inside showing the impact Mel Gibson's head whips forward as you'd expect, while his passenger's head doesn't.
Continuity mistake: When Porter, Val and Lynn make the 'hit' on the Chows in the beginning of the movie, their car changes from a 1970 Nova to a 1973 Nova. It is apparent by the differences in the grill: There are square, orange parking lights in the grill on a '73 and there are no parking lights in the grill of a '70.
Other mistake: When Porter cuts the fuel line on the car and is about to light it, Carter's henchmen see him and act surprised. Despite having ample time to get out (as any rational person might do), they just sit in the car and wait for it to explode.
Answer: Quote, "A work man is worthy of his hire." In the original version, the Mob Boss asked, "why are you doing all this?" He replied, "I want my money." It's as simple as that. He did a job and wants his payment.