The ball is moving fast enough that for at least some moves the previous person hasn't yet touched the ball 2 seconds before, you cannot block a spike if you are not in the air before the spiker touches the ball. The spiker of course will be watching you and change how the ball is spiked based on that (if you don't make any attempt to block at all the spiker will drive the ball hard into the ground, if you do it is either find the hole in your defense to spike through, or tip the ball over the blocker making the return a lot easier)

I only played at a college class level (I wasn't the best in my class, not a pro for sure) - yet I can do the above.