Here’s a little tip that will improve the quality of your conversations:
Use “What if…” instead of “Why don’t you…”
If we use “why didn’t you…” or “why don’t you…” or “why haven’t you…” I guess we REALLY want to ask the person to look at possibilities. And we usually don’t get that result, since we run the risk that the person gets defensive.
If they knew the answer to “why didn’t you…” I guess they would have done it?
What if you asked them “What if…” instead?