Truly, I say to you, there are some standing here who will not taste death until they see the Son of Man coming in his kingdom (Mt 16:28, par. Mk 9:1; Lk 9:27).
i) "Skeptics" think Jesus mispredicted the end of the world. In this post I won't attempt to discuss what I think Mt 16:28 means. Rather, I'll discuss what it can't mean. My argument doesn't depend on explaining what I think it means. Rather, it's enough to show what it can't mean.
ii) Many scholars think Mt 10:23 & 24:34 refer to the same event as 16:28. Let's grant that for discussion purposes.
iii) Minimally, Jesus appears to be saying that some of his contemporaries will still be alive at the time of the "coming" (whatever that means). It's possible that his statement has a narrower scope–in reference to the disciples–rather than his contemporaries in general.
iv) "Skeptics" think the "coming" denotes the end of the world. The problem, though, is whether that's how Mark, and especially Matthew and Luke understood the prediction. Let's say Jesus uttered this prediction c. 30. Conservatives generally date Mark to the 50s, while dating Matthew and Luke to the 60s. That would mean Matthew and Luke were written over a generation after Jesus uttered that prediction.
Liberals generally date Mark to the 70s while dating Matthew and Luke to 80-100. That would mean Matthew and Luke were written two or three generations after Jesus uttered that prediction.
That, however, generates internal tension for the liberal position. At the time of writing (80-100), how many of Christ's contemporaries were still alive? How many people who were standing there, some 70 years earlier, were still alive? How many people who were old enough to follow him around and hear that prophecy were still alive at the time Matthew and Luke were composed, according to liberal dating schemes?
What would motivate Matthew and Luke to copy a prophecy from Mark which appeared to be untenable by the time they got around to composing their Gospels? What gives? Did they understand this to be an end-of-the-world prophecy? Sometimes Matthew and Luke edit Mark, so they don't feel compelled to reproduce what they find in Mark.
v) If, moreover, they thought the end of the world was just a few years away, why even bother to write such lengthy Gospels? Their Gospels are stuffed with material that's pretty pointless if there's just minutes remaining on the timer before the bomb goes off.
Why do people need to know all that? When will they be able to make use of that?
Indeed, that's a distraction. If their readers are down to the wire, then clogging the Gospels with all this extraneous material is counterproductive. You need to warn people clearly and succinctly how to get right with God. Cluttering the Gospels with so much diverse material impedes the urgency of the warning, if the world is about to end.
By contrast, Matthew and Luke read very much like they were written for the long haul. Written for posterity.