Mind your speech a little lest you should mar your fortunes.

Also found in:

Words are easy, like the wind; Faithful friends are hard to find.

We know what we are, but know not what we may be.

It is a wise father that knows his own child.

Nothing will come of nothing.

Not in his speech, not in his thoughts, I see his greatness only in his actions, in his life.

Everything becomes a little different as soon as it is spoken out loud.

It's quite simple (public speaking) Say what you have to say, and when you come to a sentence with a grammatical ending, sit down.