I heard this story from Rabbi Elimelech Biderman:
Someone independently opened a synagogue, etc., and started to act as a Chassidic Rebbe but then began wondering if he was worthy for the position, so he went to ask the Chazon Ish.
The Chazon Ish told him that even if his mantle enables him to strengthen the Torah observance of just one Jew, it’s all worth it. Then, as he was leaving (the C.I. is known for the dramatic effect!), the Chazon Ish called him back and added: “And that holds even if the only person you’re helping is yourself!” (By the way, the Chazon Ish likewise believed anyone may, and indeed, ought to, publish their novel Torah thoughts, for the very same reason.)
This Rebbe would often repeat the words of the Chazon Ish to others, and mention how much encouragement they gave him.