Greed for the win takes the win away

Also commonly known as kyu disease, i.e. trying to kill something which cannot be killed, or other such overplays

Greedy moves fail, and your game falls apart.

This proverb stems from the first of the Ten Golden Rules of Go formulated by Wang Jixin:

Tān bùdé shèng （贪不得胜） - Greediness is not victorious (tderz)