I remember that many years ago I read a quote from John Lennon ( of The Beatles) that goes something like -" life is what happens, while we are busy making other plans". I even used it as my email signature line when that was the fashion in the early days of the internet and email in the early 1990s. I believe it is a very meaningful reminder for all of us. The statement basically implies that we lose moments of our real-life when trying to achieve success.
The word 'success' has different meanings for different people and there are books on the topic of success and how to define it for you and such, but here we are considering typical definition as related to accumulating money or power.
The famous book on new age spirituality called The Power of Now by Eckhart Tolle is also primarily referring to the same concept that sometimes we miss the present moment while perpetually planning the future or remembering the incidents of the past. Living in the moment has become a catchphrase nowadays but then again the phrase is actually misinterpreted by most people. Many people associate some reckless behavior or indulgence in fun activities as living in the moment. But living in the moment is actually not that. It does not mean 'do whatever'. It does not mean not creating any plans or associations or attachments etc. In my opinion, all of those things can still be done as normal humans living in the 'society' but with the "awareness" of the present moment, the vastness of this universe, the lack of control over our destinies.
Living in the moment is primarily about being aware. We need to accept and be aware of our immediate situation or surrounding instead of thinking about what could have happened or how it will affect the future or what we had expected to happen sometime in the past. Accept everything as it exists at the moment and everything being a part of the 'flow' without trying to fight it. It does not mean we should not plan for the future or save money for the future or plan to study some subject. We can do all of that while primarily accepting the current state and being aware of the "is-ness" of the current time and place.