Unintelligent & inconsiderate people (or communities or systems) who are associated with you can undo what you've done. It is bunkum to say everything is under your control. We live in an interdependent world & need to face the consequences of things we may not be responsible for. What matters is how you deal with your luck and get up every time you are knocked off, whilst understanding you may fall more frequently than you think (and accepting it). What ultimately matters is how long you are not willing to give up. What ultimately matters is how much of the fight is left within you and how much energy you can muster and re-build every time you fall or fail.
When it is said that Life is not what happens to you but how you react to it, there is more to it than what meets the eye. It does not mean that you can still decide every single thing and get exactly what you want despite other external influences. It actually indicates that your life could be drastically different from what you intend it to be like and you better be prepared for it. You may not get what you want at times. You may have to change your plan and approach at times. You may have to adapt yourself to a new situation almost every time something external changes it. It may still mean lost opportunities. It may still mean a change of ideas. It may still mean a change of desires.
There is a time when you can be obstinate and chase whatever you wanted to all your life, till you achieve it, despite a million set-backs and there are times when you must go with what emerges and be ready to change your own mind or desire. You must be in a position to decide what you cannot compromise on and what you will never ever give up on and what you will have to let go of in order to accommodate for the uncertainties of life.