To fully understand Myanmar traffic, you have to go back to the 1962 military coup. The new military government decided to purge the country of all unwanted relics of British colonialism like representative democracy, the rule of law, and driving on the left.
Despite neighbours India and Thailand and major car producer Japan all driving on the left, Myanmar (then still Burma) made the switch to driving on the right. However, all the cars still had the steering wheel on the right hand side. As cars became more widespread, people kept buying right hand drive cars and buses as this is what was available, mainly Japanese cars presumably coming in via Thailand. To this day, 99% of cars and buses are right hand drive and all the infrastructure (such as toll booths) are set up for right hand drive cars.
Given they are driving on the right in right hand drive cars, any overtaking is done completely unsighted, a dangerous proposition given the number of slow moving scooters, trucks, or bullock carts being on the road and the likelihood of another vehicle coming the other way doing the exact same thing.
To get around this problem, Myanmar buses employ a spotter. The spotter sits in the stair well on the left hand side looking for when it is safe to overtake, sometimes even hanging out the open door to get a better view.
There are different classes of bus travel in Myanmar, though it can be unclear which kind you are getting. Most buses will claim to have AC, but the quality of that AC is variable and on some of the buses we were better off opening a window.
The nicer buses, like for our trip from Yangon to Nay Pyi Taw, have a “flight” attendant handing out water and a “brownie”. Even on the lower quality buses you generally get handed a water at the beginning of the trip, though it becomes a calculation of how much you can drink how quickly without needing to go to the toilet (they don’t have toilets on board) but before it becomes so warm as to be undrinkable.
The cheaper buses also like to travel a circuitous route to drive past as many potential customers as possible. I think Myanmar bus companies must have engaged the guy that planned the ACTION network.
Whichever kind of bus you are on, drivers like to stop every 2 or 3 hours to cool down the engines with a garden hose. I’m not sure whether this is strictly necessary, but stretching your legs or grabbing some cold water is always welcome.