4 busts is unfortunately 4 busts for all eternity as far as your training record is concerned, but I agree with the others that you should continue training if you think it is feasible. Don't kid yourself though. If you are truly not meant to fly, by all means quit before someone gets hurt. But having a hard time with one rating may not be conclusive evidence that you cannot do it, although you are not off to a hot start. I say give it another try. The airlines do not want high bust pilots because they are expensive to train, it is not a moral thing. If you were to keep the bust count at 4 and get all the other certs with less trouble, I tend to think a hiring staff would recognize you triumphed over a learning block. From what I read here, it will probably not be an airline though because of the cost of training overhead. The bust limit for airlines is normally 3, with zero being common. Maybe 2 during a rapid growth period.