keep to oneself

Indeed, sometimes the sort of thing that might be best kept to oneself.

“But still, things of that sort are usually kept to oneself.”

Or perhaps they had just learned a lesson that Mr. Tale-Yax so clearly had not: better to keep to oneself than to risk the trouble that comes from extending a helping hand.

One should not be an artist save when one absolutely cannot keep to oneself the feeling one has—only when one has too much feeling.

One could buy expensive digital books which one was allowed to share, quote, or copy for classroom use, and cheaper ones which one had to keep to oneself.