"When in doubt, have a man come through a door with a gun in his hand." -- Raymond Chandler
One danger of applying the second is that you neglect the first. If the man with the gun is not an established character, there is neither probable nor necessary sequence in his appearance.
This is why, although Aristotle was also right when he said
A beginning is that which does not itself follow anything by causal necessity, but after which something naturally is or comes to be. An end, on the contrary, is that which itself naturally follows some other thing, either by necessity, or as a rule, but has nothing following it. A middle is that which follows something as some other thing follows it. A well constructed plot, therefore, must neither begin nor end at haphazard, but conform to these principles.
that applies to the end result, not to the writing process. You have to go back and put in the man, or excise him in revision, or otherwise smooth him out.
Though I've heard of writers who throw a random sentence in and then write on without including it in the events, just to jar things loose.