When you try to lead someone who doesn’t feel understood you ruin your your chances of leading them.
I want to emphasize in this post the difference between understanding someone and them feeling understood. You understanding someone happens in your head. Them feeling understood happens in their head. People don’t act on what’s in your head. They act on what’s in their heads.
Here’s what trying to lead someone without them feeling understood is like.
Imagine you walked into a store and before you told anyone what you wanted, a salesperson walked up to you and said “I know what you want. Here it is,” and handed you something to buy. Almost certainly they would offer you something you didn’t want. Even if they handed you what you wanted, they’d probably get some detail off, like the size, color, quantity, or whatever. Even in the unlikely case they offered you exactly what you wanted, since you didn’t tell them what you wanted, you’d suspect they had ulterior motives, like they were trying to unload something on you. Their behavior might stop you from buying the exact thing you were looking for.
Since everyone knows you do what you’re doing something for your interests, when you try to lead someone who doesn’t feel understood, they’ll presume that’s your only motivation. They’ll conclude you’re trying to use them.
Would it matter if the salesperson understood you perfectly? Maybe they did because fifty people just like you walked in exactly the same way just before you and asked for the exact same thing. That understanding happens in their head. Their understanding doesn’t motivate you.
The salesperson asking you a few questions would give you the feeling they were trying to help you. Then they have a chance at influencing you. You feeling understood benefits the relationship even if they perfectly understood you. Because their understanding has nothing to do with your mental state, and your mental state is the only one that motivates you.
In practice it’s difficult to make someone feel understood without understanding them, so you generally have to take time to understand them.

Doesn’t this take extra time?

If you understand someone, taking time to confirm may take a few seconds. You wouldn’t have wasted that time, though, because you would have helped them feel understood—that is, to change their mental state. You save yourself from them looking at you with the same suspicion with which you’d look at the salesperson who offered you what you wanted without asking your needs first. Only if you cared only about your mental state could you consider that time wasted.
If you don’t understand them, taking the time to confirm saves you from mistakenly trying to lead someone you don’t understand, which will provoke skepticism and feelings of “You don’t understand me so I’m leaving you.”