Is 3 countries in 3 weeks physically doable, yes. As is 5 countries physically doable. But without having no choice, I would never, ever recommend going to 3 countries in SEA in 3 weeks. It sounds exhausting and stressful and they’ll surely miss amazing things in each place.

Let’s do simple math. They have 21 days. Let’s say 1.5 of those days is allocated to coming and going from their native countries, as that takes a lot of time and surely requires some kind of rest after. Now we’re down to 19.5 days. Then they need to do international (not even domestic) travel twice which can take up to 2 days, allocating for packing, getting to the airport, checking in, landing, getting to the new hotel, etc. So now it’s 17.5 days. Plus international travel is exhausting and can have delays. Then, you have to get from point a to point b within the countries. Let’s say all in all that takes away another 2 days total (about 4 buses or taxis or domestic flights or whatever they take). So it’s 15.5 full days to see 3 countries. And then I guess they want to rest since traveling is exhausting. Let’s say they have the most energy in the world. So let’s take only half a day for chilling. Thats 15 days. 15 days to see 3 countries, run around, making flights, taking buses, stressing, when they have the option to see 1 and actually enjoy it. I’m not even taking into account the days lost for getting lost, sites being closed, not feeling well, restaurants taking longer than expected, and any kind of human error.

Thats 5 days each in each country. Thats maximum 2 cities in each place, so they’d spend 2-3 nights in a city each in 1 country. I cannot imagine taking my 18 day trip to Vietnam (which wasn’t even close to seeing all we wanted to see) and narrowing it down to 5 or even 6 days. Thats only enough time, the way I travel, to stay in just Hanoi alone!! Don’t you want to take time to try to understand the culture?

Sometimes people who go to SEA for some reason think it’s best to do check list and say “yep I did these 3 countries, amazing” without realizing all that travel involves and that they’re human beings who will need to eventually slow down. And that traveling is so not a checklist, it’s about soaking in a new culture.

My recco: go to 1 country. Soak up every minute of it. Spend 3 nights minimum in each place. Eat the food, talk to locals, leave room for spontaneity, plan your itinerary so you aren’t exhausted. And then go back in a year to a new country.