Answer:
The sources are various documents written by the OECD: The Organization for Economic Co-operation and Development, and official sources made by the Government of Liechtenstein.
There are many reasons why Liechtenstein has such a high GDP Per capita. The first reason is its political system, which is surprisingly federal, even for such a small state. This means that the different municipalities of Liechtenstein compete among themselves for investment and development, for example, by offering lower tax rates.
The second reason is precisely the economic incentives that the country offers to private businesses. Relatively low taxation, very good infraestructure, well-educated human capital, and closeness to the wealthy markets of Germany, Switzerland, and Austria are among the economic incentives that make Liechtenstein a country with more companies registered (around 70,000) than inhabitants (around 38,000).