The man at Scholagladiatoria put out a good video about results vs. strategy today.
What he's talking about is valid for any conflict scenario, be it in combat or gaming or writing a story. Plans are the decisions made using the available intelligence. They cannot, and therefore do not, have perfect information to work with. That means that there is always room for doubt as to the plan's effectiveness, and that's before the factor of execution.
The results of the plan are independent of the quality of the plan. Those executing it may screw it up, in whole or in part. Unforeseen events may force alterations to the plan, both for and against you. The information used to generate the plan may be wrong, innocently or not, so the plan's premises are false. All this can more can, and will, make plans that seem to guarantee success fail; it can also make piss-poor plans produce positive results. That's what the man's getting at here.
Keep this in mind when you see someone attempt to form and execute a plan. Most of us are not this man, but we can all agree with his catchphrase.
And whatever you do, never be this man. He died for his stupidity. Valhalla is not open to you, Staaden, for you are a Gamma faggot.