The expression “don’t put all your eggs in one basket” is a fairly old-fashioned English expression which does not relate to animals but is used as a warning relating to making assumptions that something will happen.
The expression is used to warn someone about pinning all their hopes on something and assuming that something will work out and therefore focussing all their effort on that one thing. The warning given is that if you do this you risk losing everything!
The earliest recorded English usage of this expression can be found in the Oxford Dictionary of English Proverbs in 1710 which reads “Don’t venture all your eggs in one basket.” There is, however, an earlier usage of an expression with the same meaning as this which does not exist in English nowadays but may have been used as the inspiration for the expression. It reads “He is a fool which will adventure all his goods in one ship”, and can be dated to 1617.
The premise of the idiom comes from the very practical idea that if a farmer collects all his eggs in one basket and he drops the basket on his way to store the eggs then he has essentially lost everything he worked for and will have to start again from scratch whereas if he had split the eggs between two baskets the consequences would have been limited.
An example of the usage of this idiom can be found in Miguel Cervantes’ novel of 1615, “Don Quixote” which reads “it is the part of a wise man to keep himself today for tomorrow, and not venture all his eggs in one basket.”