patterns and practices – Who should log output, the ThingDoer or the code which calls ThingDoer.DoThing()?

Here’s a common question I ask myself:

If I have a ThingDoer class and it has a method DoThing(), and I want to log a message stating “Doing a thing”, should I put this logging code in the ThingDoer.DoThing method, or should I keep this code outside of the method, within the caller? I feel like there should be some standard principle to follow here but I don’t know what it is.

Log("Doing Thing");
ThingDoer.DoThing();

vs

void ThingDoer::DoThing()
{
    Log("Doing Thing");
}