one shouldn`t risk losing something certain by trying to get something that is not certain You should keep the prize and not try and win another one. Remember a bird in the hand is worth two in the bush.
BIRD IN THE HAND IS WORTH TWO IN THE BUSH
Meaning of BIRD IN THE HAND IS WORTH TWO IN THE BUSH in English
English idioms vocab. Словарь английских идиом и выражений. 2012