Jesus told the apostles that just as they were able to observe the time of year from the obvious and predictable cycles of nature  (Matt 24), we also will be able to recognize the coming end to this age.  That is, the attitudes of men, and the way they choose to live will clearly indicate our proximity to the end (Matt 24 ).
 
In Mark 13:17-31 Jesus warns the apostles that in only a short time they would not only abandon Him, but as in Peters case deny that they even knew Him. These men, Jesus' closest friends, on the night before His crucifixion, still couldn't grasp what was about to take place.  Even Jesus' own prophetic words pointing them towards His death, the event for which He was born, were met with an self-assured, rejection that such a thing could never happen.  As we look back to those events we might ask "How could they not see what is now so clear to us?"