Nothing should happen at random. Every element in a story should have significance whether for verisimilitude, symbolism, or the intended climax. Names, places, actions and events should all be purposeful.
Plot stems from character under adversity.
And the stress itself must also be plausible, given the circumstances of the story. Each character has an urgent personal agenda. Too much is at stake to abandon that agenda without good reason. We may not share the character's urgency, but we should be able to see why he cares so much about what he's doing. The plot of a story is the synthesis of the plots of its individual characters.