Do not dedicate all your resources to one project. / Do not count on any one thing to safeguard what is valuable.

The bearer of bad news should not be held accountable for it.

A response indicating that one is either unwilling or unable to perform a task, or that one is not guilty of something for which blame was implied.

(idiomatic) Used to attempt to avoid or abbreviate a discussion that speaker or hearer may wish to avoid.

A polite way of responding to thanks, by suggesting that the service is too trivial or humble to warrant thanks; you're welcome. / Used other than figuratively or idiomatically: see don't, mention, it.

(idiomatic, often humorous) Somewhat sarcastic but usually good-natured advice used to criticise a person's degree of talent (especially in music or other performing arts), implying that he or she could not make a living from it.

(US, dated) Do not permit yourself to be cheated or duped; do not be naive.

(ethics) A wrongful action is not a morally appropriate way to correct or cancel a previous wrongful action.

To say that somebody is not to do anything without receiving further instructions. / To say that somebody is obliged to do something without question.

One should not unappreciatively question or inspect a gift too closely.