yep. It's a small country but it's the oldest democracy on the continent, ranks quite highly internationally (30th on the democracy index, ahead of Italy), and has a gdp per capita only slightly lower than the baltics (20k). By most accounts a pretty tremendous success.

> has a gdp per capita only slightly lower than the baltics (20k)

Your numbers are not even close.

> In 2019, the GDP per capita (adjusted for purchasing power parity) was $36,701 in Lithuania, $35,853 in Estonia and $30,830 in Latvia.

Source: https://wedc.org/export/market-intelligence/posts/strong-gro...

Botswana has a $7,347.55 GDP per capita according to Google (in 2021).

That's at least 75% lower than the worst Baltic nation, not "slightly below."

Any obvious reasons why it has enjoyed this success while its southern neighbour hasn’t?

It's a tiny country (population 2.3 million, vs South Africa's 60 million), mono-ethnic, rich in diamonds, strong culture of law and order.

South Africa also props Botswana up via a customs union.

https://www.tralac.org/news/article/6931-surge-in-botswana-s...

Competent forward-looking leadership.

There's plenty of factors that helped, I can think of a dozen right off the top of my head, but the one that made a crucial difference is in my opinion really the above.

Basically this: https://en.wikipedia.org/wiki/Seretse_Khama#Presidency

And this: https://www.tralac.org/news/article/6931-surge-in-botswana-s...

Hasn't really developed, it just has a tiny population while also having a lot of diamonds. Its economy is still almost entirely extractive.

It's probably best compared to something like Qatar, where the hope is it'll be able to use the diamond wealth to found another industry.