Whoah! Holy blown out of proportion! I didn't say that marriage is for everybody, and I certainly didn't say run out and get married because you may be lonely. Both of those would be ridiculous statements. Get married if you find someone you love and it's something the two of you want to do. Do it for no other reason.
All I said is that stuff can happen quicker than you think, and it's hard to plan 5-10 years down the road at this stage in your life without things constantly changing. Plans like that tend to be ephemeral and priorities change... Will they change for you? Maybe or maybe not. I'm not you. I, personally, got tired of coming home to an empty apartment, and fortunately enough found a girl I really liked who apparently really liked me. All I can share are my own experiences as someone who was happily single at 26 with no prospects of being otherwise and am now happily married at 29.
I will say, however, that unless you make a HUGE conscious effort during residency, it will be difficult (again, not impossible) to have lots of friends outside of the residency program (due to your hours, flipping nights, call, etc.) You can do it, and some do, but it's hard. Most of my friends outside our program are through my wife, and I can't do a lot of the things they do together because of my schedule. From what I've seen (again this could be different at different programs) it's also hard to "get everybody together" as a residency program. Factor in that someone always has to be manning the department(s), (around) half of the residents are on off-service rotations with a completely different schedules, etc. Also, as you yourself said, lots of people this age are busy with their own new families and have their own commitments outside of the residency. It's certainly not the only option, but it's naive to say that just because the option isn't right for you, it's not what other people want. I always wanted a family, and hopefully that will work out for us when we're ready.
Just a quick little aside to finish up this novella: When I was a first year medical student (on our first day actually), our dean of student life told us something that has always stuck with me. He said, "No one ever looks back from their death-bed and thinks, 'You know, I wish I would have spent more time at work...'" Having seen a lot of people die over this crazy ride through medicine, I have to agree.
If you made it through all that I'm impressed. Sorry if it sounded a little preachy.
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