People trust the recommendations of someone who’s told them “this isn’t for you” before.

Enthusiasm about everything is indistinguishable from having no opinion. If you have never advised against anything, nobody can tell whether your approval means much, because it has never once been withheld. A single honest discouragement makes every recommendation after it worth listening to.

Say so the next time you think something is not right for somebody, even when they are hoping to hear otherwise. Be clear about why, and leave the decision with them. You are building the thing that makes your yes useful.