Talking to those who won't listen
Why, when the messengers told Lot that God was going to nuke the Greater Sodom Metropolitan Area, did he immediately believe them?
I mean... Lot wasn't exactly a frum guy. Given his options, he chose to live in Sodom. He seems not to have learned a lot from Avraham Avinu, and what he did learn, he got messed up. He offered hospitality to the messengers (good), but offered his daughters up to the mob in order to protect them (bad).
And yet, consider the difference between Lot and his sons-in-law. When he tells them that the end is nigh, they laugh in his face. What's going on? After all, Lot and his sons-in-law aren't really all that different.
The difference is that Lot heard Avraham Avinu. He may not have paid a lot of attention to what Avraham Avinu said. He may have rejected it. But he heard it. And as a result, when the time came, that seed, left there inside of him, was able to sprout enough for him to hear what God's messengers were saying.
A lot of the time, it feels like telling the truth in an environment where people just aren't listening is a waste of time. Sometimes there's a great temptation to sacrifice the truth of your position in order to get people to meet you half way. But this only teaches them that even you don't really stand by the truth you claim to believe in. It's ultimately counter-productive, even if it feels like it's resulting in positive results in the short term. One Modern Orthodox rabbi has argued in favor of that approach with the question: "Are you trying to win arguments or people?" But that's more than just a false dichotomy. In the end, fudging the truth in order to win people doesn't work. They don't stay. And in my almost never humble opinion, doing that is a form of flattery, which the Torah forbids.