"For we all often stumble and fall and offend in many things.
And if anyone does not offend in speech [never says the wrong thing], he is a fully developed character and a perfect man, able to control his whole body and to curb his entire nature."
James 3:2 AMP

If we can control our mouth, we can control our body and entire nature. James gives us information about the tongue. We can apply his words to our own life.

The problems we face come from within, our resistant will, the lusts of the flesh, etc. And they come without, symptoms of illnesses and accidents may come against us.

The principle holds true; as we control our mouth, we can control ourselves inside and out.