Why do some friendships survive the test of time while others don't? Can a lost friendship be revived?
We met in the autumn of 1990, in the United States.
The US was having its midterm elections and a group of about 30 of us were invited to tour the country for a month.
We were a mix of journalists, Members of Parliament, academics and political party activists.
We came from countries the US thought would benefit from witnessing democracy at work, among them Cyprus, Egypt, India, Ireland, Israel, the Maldives and Nigeria.
While not as exciting as a presidential election, there was still plenty of mudslinging between the Democrats and Republicans, as they fought for seats in Congress.
It was a heady four weeks as we visited six cities around the country. The travelling and excitement bonded us. We got along well, had a fantastic time and were sad when we had to say goodbye.
As happens in groups, some people got along better with each other and would hang out together more.
One of those I clicked with was D.
He and I came from very different worlds, but maybe because we were single and among the younger ones in the group, we could talk. We laughed at the same jokes and were comfortable in each other's company.
When the trip was over, we kept in touch through letters - yes, it's hard to imagine, but those were the days before e-mail.
Then, as in most long-distance friendships, ours died after a while.
We were busy with our own lives, we lived too far away from each other and we didn't have that much in common other than the American trip, which was becoming a pleasant but distant memory.
In 1994, though, we met up.
A Singapore minister visited his country and I was one of the journalists who covered the trip.
D picked me up late one night after I'd filed my stories and we went for drinks at a hotel.
We sat in a candle-lit courtyard but after the initial burst of catching up, the conversation dragged. There wasn't much to say to each other beyond recollecting our American adventure.
And so, I thought, that was that, then. Like so many other friendships in my life, it was good while it lasted but the journey must end sooner or later.
Two years ago, out of the blue, I got an e-mail from him to say he would be in Singapore for a working trip. Was I free to meet? Unfortunately, I had to travel at the time and replied that I couldn't.
Then last week, he visited Singapore again and, this time, we did get together for dinner.
I didn't meet him alone though.
H came along.
I'm not sure how other married couples would approach a situation like this, but I didn't feel I should be meeting a friend of the opposite sex alone for dinner.
In any case, I thought it'd be interesting for them to meet.
H took a bit of persuading but, in the end, he said he'd come along if I wanted him to.
I was worried things would be awkward, but the evening turned out fine.
I wouldn't say the two men got on like a house on fire, but the vibes were positive and they discovered a common interest in football.
As for me, I was happy to see D after 22 years.
It brought back memories of the trip and how I was young, crazy and carefree then.
He had got married soon after we met in 1994 and I was happy to learn that he and his family - he has two sons - are doing well. He showed us pictures of them.
It was interesting to observe how he had changed in those intervening years.
We both exclaimed how we were the same but, of course, we weren't, physically, mentally and probably spiritually too.
The meeting was bittersweet somehow.
There's nothing like meeting someone from your long-gone past to drive home how you are so much older now.
I could see it in his eyes - and he in mine - that we have both lived through so much. We have become different people and moved on with our lives.
Even if we wanted to go back to that easy friendship we once shared - and I am not sure we did - we knew it wasn't going to happen.
Yet there was a bond because of the friendship that once was, but now was lost.
I felt rather sad even though I knew I shouldn't because I was, after all, meeting an old friend.
Friendship is such a strange thing.
There are people you have known for decades but don't consider friends, yet others you meet just once and know you've found a kindred spirit.
What is it that makes us like another person? Friendship, after all, must be rooted in like.
Is it a certain look, a feeling he or she evokes in you, a smell even?
Why do we feel at ease in one person's company, but are petrified to be alone in another's?
Why do some people give you a warm, fuzzy feeling when you bump into them on the street, and why do you feel like fleeing the scene when you spot another person?
And when you do become friends with someone, why do some friendships last forever, others for a period of time, and then there are friendships that die a quick death?
Over the years, I've come to some conclusions about friendship:
• You can't force a friendship. It's either there or not and the desire to be friends has to be mutual.
• A friend - or a spouse - of a friend doesn't necessarily become your friend too.
I've always been intrigued by how there are people I like- and who like me - who have friends whom I would not want to be friends with, and, in fact, whom I positively loathe. How is that possible?
• Sometimes, you outgrow a friend. Sometimes, the friend outgrows you. When that happens, let it slide. People change, you change. You shouldn't feel guilty or take it personally when a friendship fizzles out.
• It's okay to shed old friends. Just because you've been friends since the age of five doesn't mean you are obliged to still be friends at 50, if you don't feel like it. Maintaining a friendship that has become stale and suffocating is a waste of time for both of you. Life is short. It's fine to move on.
• It's okay to make new friends. The best thing about new friendships is how they don't come with baggage. It's a chance to start anew, to present yourself the way you want to be seen now, not how an old friend pictures you.
• Marriage changes friendships. It especially complicates friendships you had with the opposite sex before you got married. You also have to navigate your spouse's friends, whom you might not want to be friendly with if you had a choice.
After our dinner with D, I sent him an e-mail to wish him well. Take care, I said, and keep in touch.
He replied to thank me for dinner and also said we should keep in touch.
I wonder if we will or if we were just saying it because that's what people say after they meet old friends.
But I really shouldn't think too much into this.
We had a friendship once and it made us happy then.
Even if we don't keep in touch, I'm grateful for that friendship. If that's as good as it gets, then it's good enough for me.
• Follow Sumiko Tan on Twitter @STsumikotan
A version of this article appeared in the print edition of The Sunday Times on July 17, 2016, with the headline 'A friendship from the past'. Print Edition | Subscribe
We have been experiencing some problems with subscriber log-ins and apologise for the inconvenience caused. Until we resolve the issues, subscribers need not log in to access ST Digital articles. But a log-in is still required for our PDFs.