There are always 36 "hidden" righteous people in the world at any given time. The source given for this is the Gemara in Succah 45b. Nefesh Adoni says "אין העולם מתקיים ועומד אלא בזכות ל"ו צדיקים נסתרים", so we see they're hidden. My question is how does one know if he's one of these tzaddikim?
The problem is how you define a tzadik. Most people see a tzadik as super wise and smart person like Rav Herschel Sechter shlita and Rav Chaim Kaniefsky shlita. They are both gedolim but what makes a tzadik is someone who fullfills his own unique potential. His potential may be small but he is still considered a tzadik.
This is how you must understand the rambam in Hilchot Teshuva 5:2 also read the kesef mishna.
You may not know your great, but each person is not expected of the same thing. Not everyone would know that they are one of the 36 hidden tzadikim. Like the butcher and the rabbi. https://www.chabad.org/library/article_cdo/aid/2271173/jewish/The-Butcher-in-Heaven.htm