Matthew and Mark offer two different renderings of the same account.
(Matthew 19:16, 17) . . .Now, look! a certain one came up to him and said: “Teacher, what good must I do in order to get everlasting life?” 17 He said to him: “Why do you ask me about what is good? One there is that is good….”
(Mark 10:17, 18) . . .And as he was going out on his way, a certain man ran up and fell upon his knees before him and put the question to him: “Good Teacher, what must I do to inherit everlasting life?” 18 Jesus said to him: “Why do you call me good? Nobody is good, except one, God.
Now a) this may not be the same account, but two instances of a similar occurrence, or b) it is the same account, but elements are omitted from each account, or c) the truth isn’t in the precise relating of what was said but in the essence of what was said.