In (one's) (own) interest noun phrase
The phrase can be rewritten as "in the interest of one" or "in one's best interest".
In order to bring advantage or benefit to somebody
It would be in your interest if you are proficient in the second language.
The people have supported policies in their interest.
A plan, project, development, or course of action that seems to have no meaningful, desirable, or useful conclusion
To be beneficial to someone or something
The phrase dates back from the early 1700s
A problem or difficult circumstance
I'm short-sighted, so forgetting my glasses is a real hair in the butter for my sight.