Who writes the script ?

Have you ever thought that you should have been given a bigger part to play in the real life game ? Or maybe you think you have missed the bus and turned up at the rehearsal for a different game ?
In these rehearsals you can make mistakes, forget the lines or any number of other false steps but without serious consequences.
However there are no such options - once your game starts its live and you have to take part and  a complex series of decisions have to be made.
You possibly have guessed already - you have to write your own script.
There are exceptions to this rule as there usually are to all rules - you can be born with the proverbial 'silver spoon' and your script is already written - we'll call these people 'spongers' and we would all know who they are just as we know that we are unlikely to be joining their ranks.
  It would not be advisable to have 'a plan '. (Think Brexit ) Things can go wrong and this then requires a plan B,C etc,etc.

So the best option might be to anticipate change and make only a brief outline of where you are trying to get to and alter the strategy as and when circumstances change. This should help you to stay on course and would not have such a serious impact as having 'a plan' - To sum up you could say that having ' a plan ' is traditionally more suited to the 'spongers' ( Think Brexit again & its main advocators ) and why would you want to be one of them?