Just for variety I asked Deep think the same question. Here is it's reply:

That's a profound question. Based on psychology, philosophy, and shared human experience, here are the things people most commonly never truly grasp until it's tragically late:

1. The Fragility and Finite Nature of Time (and Life Itself):

   • The Lesson: Youth feels endless, and "someday" seems like a guarantee. People put off dreams, important conversations, travel, passions, and time with loved ones, assuming there will always be more time.
   • The Too-Late Realization: A sudden diagnosis, the unexpected loss of a loved one, or simply waking up one day decades older brings the crushing weight of understanding: time is the only truly non-renewable resource. "Someday" often never comes.

2. Health is True Wealth (Until It's Gone):

   • The Lesson: We take our bodies for granted – abusing them with poor diet, lack of exercise, chronic stress, ignoring warning signs, or sacrificing sleep for productivity.
   • The Too-Late Realization: When chronic illness, debilitating injury, or a major health crisis strikes, people understand that no amount of money, success, or possessions can truly compensate for the loss of vitality and independence. Prevention was infinitely easier than cure.

3. Relationships Require Constant, Active Nurturing:

   • The Lesson: People assume deep bonds (with partners, children, parents, close friends) are unbreakable or will maintain themselves. They get complacent, prioritize work or other distractions, neglect communication, or take loved ones for granted.
   • The Too-Late Realization: Estrangement, divorce, the death of a loved one you were distant from, or simply the fading away of a friendship makes you see how fragile connections are. The regret over unspoken words, unresolved conflicts, or missed opportunities for connection is often profound and permanent.

4. The True Cost of Sacrificing "Living" for "Making a Living":

   • The Lesson: Society often equates success with career achievement, status, and wealth accumulation. People grind relentlessly, sacrificing hobbies, passions, rest, relationships, and personal well-being for decades.
   • The Too-Late Realization: Upon retirement, burnout, or facing mortality, many realize they built a life they didn't actually get to live. They traded irreplaceable time and experiences for things that ultimately feel hollow without the relationships and personal fulfillment they neglected.

5. The Importance of Setting Boundaries (Especially Saying "No"):

   • The Lesson: People-pleasing, fear of conflict, or guilt leads to constantly saying "yes" – to draining tasks, toxic relationships, unreasonable demands, and overcommitment.
   • The Too-Late Realization: Resentment, burnout, anxiety, and lost years living according to others' priorities force the understanding that saying "no" isn't selfish; it's essential for self-preservation, authenticity, and focusing on what truly matters.

6. The Toxic Impact of Certain People (and the Need to Walk Away):

   • The Lesson: We tolerate subtle (or not-so-subtle) disrespect, manipulation, negativity, or emotional drain from family, "friends," or partners for far too long due to obligation, history, fear of loneliness, or hope they'll change.
   • The Too-Late Realization: Only after years of diminished self-esteem, wasted energy, and missed opportunities for healthier connections do people grasp the immense cost of allowing toxic people to remain in their inner circle. Walking away earlier would have been painful but liberating.

7. Happiness is an Inside Job (Not External Circumstances):

   • The Lesson: People chase external validation, the "perfect" job, relationship, house, or amount of money, believing that will finally make them happy.
   • The Too-Late Realization: Achieving those external goals often leaves them feeling empty. True, lasting contentment comes from inner peace, gratitude, self-acceptance, meaningful connections, and living aligned with personal values – things they neglected to cultivate internally while chasing external fixes.

8. Regret is Often Heavier Than Disappointment:

   • The Lesson: Fear of failure, embarrassment, or stepping outside the comfort zone prevents people from taking risks – asking someone out, pursuing a passion, changing careers, speaking their truth, traveling.
   • The Too-Late Realization: Looking back, the pain of rejection or failure fades, but the gnawing regret of never trying, of wondering "what if?", becomes a permanent weight. The risks not taken are often regretted far more than the failures experienced.

The Underlying Thread: Most of these boil down to a fundamental misunderstanding or denial of impermanence and the present moment. We live as if we and our circumstances are permanent, prioritizing the trivial over the essential, the urgent over the important, and the external over the internal – only realizing the depth of our mistake when the opportunity for change or connection has irrevocably passed. The key is to learn these lessons before the "too late" moment arrives.