You ask a very important and pertinent question. It’s very hard for us to watch our kids make their mistakes, as they inevitably must (as we did before them). But unless it is life threatening or dangerous in some other way to their well-being, parents should let their kids find their own way UNLESS asked for their input. Just as we did not want our own parents interfering, our kids feel the same way. Kids who respect their parents’ wisdom and experience will ask for advice if they need it. It is for THEM to “improve their ways” not for us to do it for them.
It’s so hard to bite our lips and refrain from comment when we see what we “know” is a big mistake on their parts. Even when we might be right (purchasing a house that is a bad deal, making a bad shidduch, buying poorly made furniture, etc.)we have to be very careful how we word our comments, so they will not be resistant to hearing what we have to say.