The first one gets the oyster, the second gets the shell. – Andrew Carnegie

This quote is true in many industries, there is even a well agreed upon consensus about  first-mover advantage and the associated gain in market share. First-mover advantage or simply First-to-market, means being the first not necessarily to launch a new product, but to gain consumer confidence and hence market share.
A product can be launched in a bad form, thus would be ignored by masses. But once a product is properly launched, the first company to do so would gain significant market share. Any subsequent company offering a similar product will have an uphill battle to wage.

The first one gets the oyster, the second gets the shell.

– Andrew Carnegie

From this context, the first company gets the bulk of the market share “oyster”, the second will get insignificant share of the market “shell”.

A nice example here is Coca-Cola and Pepsi Cola. Pepsi had to make huge efforts to convince the masses it is better than Cola, and it failed.
Even in one marketing stunt, Pepsi blind folded the customers and made them test and chose between Pepsi and Coca-Cola.
When most customers realized they chose Pepsi, they would switch choice pretending they actually made a mistake and they do not like the Pepsi one better.

First to market, create an association between the product and the brand, that is very difficult to undo!

About Andrew Carnegie:
Andrew Carnegie was a Scottish-American industrialist and philanthropist. Carnegie led the expansion of the American steel industry in the late 19th century and became one of the richest Americans in history. He became a leading philanthropist in the United States and in the British Empire.