But there is a deeper countdown which has already started and is going to reach the end point but no one knows when, its the countdown of Life !!.. It began the day we were born and remains on till the moment we take our last breath. It would have been great if we could hear the counts so that we manage our life actions accordingly. But unfortunately the count down is silent one and I think god wanted it to be so.
One of the famous stories which I can think of about relating to this idea is from Mahabharata. During exile, once four other Pandavas happened to drink water from a lake, which was haunted by a Yaksha. Yaksha had warned them that they should answer his questions before they drink water, but none of them paid attention and were eventually got killed. Yudhisthra went there and agreed to answer all the questions, yaksha said if you answer the questions correctly then he give life to all his brothers. He asked many questions to Yudhisthira and he got good answers, one of the question was " What is the greatest mystery / Paradox/ wonder of life ? Ans by Yudhistira was : "We all know that we are going to die but we behave as if we are immortal" Now there are many versions to this text but the idea is quite clear and relevant in todays world.
We happen to postpone many things to tomorrow, next year, once I have xyz then Ill do it etc. But we don't realize the silent countdown is on. We have many things we want to try out / do / experience / talk to, so many things which we postpone it to some wonderful (ideal) day in future. I would like to admit that I do the same thing all the time, but I am really trying to resist it whenever possible.
Follow your passion is more or less has become a Career Gospel in today's world. It is astonishingly appealing concept, but in my personal experience says that its not so simple as it sounds like. There are many other concepts like "Purpose is more important than passion" which means finding out a cause which you value / problem in the world which bothers you and then contributing your life to do it.
I have come across many videos and articles which are very convincing about various ideas relating to this concept but I don't want to list them here. The only thing I have realized or rather have continuously come across events which rebuilds my realization is that "Success is a personal thing, we have to define it for ourselves, because if we leave for others (so called Society) to decide we would never accomplish it. The reason is the one who taught society punctuation marks forgot to teach "." (Full Stop). Society will always point towards the grass which according to it is greener, than yours.
I am very sure I have confused you, though it was not intentional. The moral of the story is "Its your life, do what you always wanted to.. its good to fail ..and blame your self for the wrong decisions you made rather than, getting carried away by the ideas which look right in the eyes of others and end up making you feel incomplete."