Three things call a person's sins to remembrance: a leaning wall, scrutinizing one's prayer [expecting it to be answered because one prayed with concentration], and handing over judgment against one's fellow.
Three Things That Bring a Person's Sins to Remembrance
Yalkut Shimoni on Torah 79:5
שְׁלֹשָׁה דְּבָרִים מַזְכִּירִים עֲווֹנוֹתָיו שֶׁל אָדָם, קִיר נָטוּי וְעִיּוּן תְּפִלָּה וּמוֹסֵר דִּין עַל חֲבֵרוֹ.