[to oneself(1)] {adv. phr.}
1. Silently; in the thoughts; without making a sign that others can see; secretly.
* /Tom thought to himself that he could win./* /Mary said to herself that Joan was prettier than Ann./* /Bill laughed to himself when John fell down./
2. Without telling others; in private; as a secret. — Used after "keep".
* /Mary keeps her affairs to herself./* /John knew the answer to the problem, but he kept it to himself./