Possibly refers to what could be done, what could occur or what could be true. It stems from the Latin term possibilis, which derives from posse, which means ‘power’ or ‘to be able to’. It is a synonym of ‘potentially’.
Probably refers to what is likely to be done, what is likely to occur or what is likely to be true. It is a statistical term used in chance to define the extent to which an event is likely to happen; hence the phrase, ‘on balance of probabilities’.
Definitely refers to what will be done, what will occur, or what will be true. It is a matter of certainty and is used to express complete agreement or strong affirmation. It is unambiguous.
Possibly, is the answer to the question, ‘Could you achieve whatever it is you want?’
Probably is the answer to the question, ‘Should you expect to fail at some point along the way?’
Definitely is the answer to the question, ‘Will it require you to be willing to change your tactics or your plans and adjust your approach from time-to-time?’
From the raft of opportunity which lies before you and the potential it offers, it is in accepting the likelihood of failure along the way and the certainty for the need to adjust your course, which will most likely result in you arriving at your desired endpoint – and realising that potential.