I have this avocado pit that I have been growing for 2-3 months. It had a big strong root, and then a strong stem came out. After about 1 cm it stopped and died.
Then another, thinner, stem came out, and this one apparently died too. And there is another one after that which still looks pretty good but maybe I have to do something to keep them alive after 1-2 cm.
I have to mention I have started with the toothpick suspended in water method and then I just added soil gradually. Also, I have 3 other avocado trees that are about 20 cm (8 inches). (https://i.stack.imgur.com/3vZRY.jpg)