(Bear in mind I'm going into biomedical research, which is a very different field than CS or Entrepreneurship, which seem to make up the majority of HN users)

For me it's not the fear of not fitting in, per se, but the loneliness that comes with being misunderstood by those around you.

I find that the point he made of not being understood when I started to pursue my career aspirations rings very true. I wouldn't blame others' inability to understand on ignorance so much as lack of experience, in that not that many people have experienced the biomedical research field for themselves, so therefore have no way of understanding the nuances or the lifestyle of it all beyond hearsay.

That lack of understanding in turn leads to an inability to connect with me, or conversely, an inability for me to connect with most people. My career takes up the majority of my time and thoughts, and as a result is one of the most important aspects of my own life. When people are unable to understand that, they in effect do not understand me as a person.

Furthermore, there's the fact that I and other people who want very badly to accomplish their dreams are often very hardworking. A bit anecdotal, but I've also found that the people who are physically in my life are by far not driven to work as hard as I do. I find a sense of happiness working 12 hours in a research lab and coming in on weekends. The "average" person in my life, however, is the sort of person who looks at a career as a means to make money; a commitment they only have to fulfill between the hours of 9AM and 5PM on weekdays. Anything beyond that (time after work, weekends, etc.) should be dedicated to partying and the like.

Going back to the point I was making before: these differences in personalities between myself and almost everyone in my life makes it almost impossible for me to truly connect with someone.

And for reasons I can't really explain beyond "human nature", even though it makes perfectly logical sense to focus on my work and be as efficient as possible, I find that interpersonal connections to be something I cannot live without. For me, there is immense comfort to be had in being able to talk to people about your life (which again for me mostly revolves around work) and have a true understanding of it all.

I'm very lucky enough to have a small yet very close group of friends who are like that (although mostly online due to college; thank you internet). However in the past two years I've already fell out of contact with most of my friends because of my shift from (and I do apologize as I can't think of a better term) a commonplace life to one that is unorthodox to most people. So a big lingering fear of mine is, "If I continue on with my goals, will I still have anyone in my life I can connect with?" While so far the answer has been "yes", the past two years still leave a very strong, lingering fear in the back of my mind. And while it's very true that I've come into contact with and maintain a personal relationship with many people above me and have gone through the same path as me, for me it's no replacement for having people in your life that are going through the same life challenges that you're experiencing yourself. As the saying goes, "Misery loves company".

On a more minor note unrelated to the article, another sort of fear I've felt (and am still feeling) is really fear of the unknown. I was the sort of person who did just enough in my life. I'd go so far as to say I was complacent with myself. This whole lifestyle of being ambitious, proactive, and actively and constantly working towards a dream that once felt unobtainable to you is all a new experience. Others above me/more experienced than me have told me stories about their own lives but in the end actually going through with the life yourself is completely different than hearing stories about it. For me, everything I'm doing now is new, unfamiliar, unknown, and as a result it's nerve wracking and scary.

While I know that everything above is not universal and there will be others on HN that have different experiences/viewpoints, these are my honest viewpoints shaped by my own experiences in my life. I hope this helped with your question.