like threading a needle

1. Passing (or passing something) through some small opening or passage, similar to thread being passed through the eye of a needle. Getting through those hulking defensemen will be like threading a needle. Good luck! An angioplasty is basically like threading a needle—you insert a catheter into the patient's artery and move it through to the blocked blood vessel.

2. By extension, requiring delicate care and thoughtfulness. Trying to motivate your students sometimes feels like threading a needle—you need to strike the right balance of tenderness and intensity.