Both these factors make up for poor communication. If a plan is based on wrong assumptions due to insufficient data or even misunderstood data then the drive towards execution will be a disaster from the start. A relatable example would be miscalculating financial estimates or even the number of people required for executing the plan.
An example of a personal goal could be something like wanting to travel to certain destinations without laying out an itinerary or budgeting your travel costs properly.
Likewise if a plan is too difficult to explain to others, how can you hope for effective communication and the desired result? When plans are not effectively capable of being explained given their complexity, team members cannot be expected to carry them out as intended.
A plan that has too many contingencies or restrictions will not only become too hard to follow let alone implement. Another reason why perfectly good strategies fail to take off.