Student or Learner
"Too often this is made a part of a post mortem when it should be part of planning."
what does it imply
In this case "post mortem," a synonym for autopsy, means analyzing what went wrong (with a project, plan, etc...). Therefore, in this case something like having enough people involved, or checking traffic and weather, or investing enough money should have been thought of as part of the planning stage of a project rather than part of the anaylsis after the project has failed.