People often interpret “I understand” to mean “I agree”, but they don’t mean the same thing.
“I understand” means someone perceives the meaning of your opinion. “I agree” means someone also shares your opinion.
It’s a subtle difference, but significant for a few reasons.
First, people hesitate to express they understand something because they’re afraid it’ll be misinterpreted as agreement. People do, indeed, misinterpret it that way. Confusion about the difference causes communication failure.
Second, people often think they want agreement when actually they want understanding. They may look like they’re out to change someone’s mind, but in reality, they just want to be listened to and understood. Confusion about the difference causes frustration.
It’s perfectly fine to disagree. Differences in values often make it impossible to reach agreement. But, with the right attitude, it should always be possible to reach understanding.