I heard a story from a local shliach. I missed the beginning (or said lechaim and got distracted), but the nekuda was that before the Rebbe would leave his room to come down for davening, the door would be half-open, and rabbi Groner would manipulate the door in such a way that nobody could see the Rebbe before he was ready to come out.
The shliach (as a young bochur) and his father were standing outside the door and waiting for the Rebbe (again, I don’t remember the details). Suddenly, rabbi Groner accidentally let the door go or something, and it swung open. They saw the Rebbe standing without his hat, without kapotta, with his color up, putting on a tie. The shliach’s father’s face became completely white. The shliach himself, he says, felt completely terrified. The Rebbe looked at them for a couple seconds, and then a big smile came to his face.
At that point, Rabbi Groner swung the door back closed. In a few minutes, the Rebbe walked out with two siddurim — one for himself, and the other for the bochur (the shliach). He looked at the father and said: “What you saw was no big deal.” Then he turned to the bochur and said: “Un du — du dorf lernen Chassidus” (“And you — you have to learn Chassidus”).
The point is: the Rebbe was confident in the shliach’s father. When you’re an emesdike person, if you meet with Emes, you can handle it. And you — who doesn’t yet know how to deal with the truth — you need to learn Chassidus.