Once, while davening, Reb Menachem Mendel of Bar, who was one of the talmidei Baal Shem Tov, thought to himself: "How can I daven to Hashem when I am so full of aveiros?" He figured this was a holy thought until he pondered it for a while and realized that such thoughts never bother him while he's eating, only while davening, so it must not be a real holy thought. He immediately banished this thought from his mind.
There is much to learn from this small story, as from every story of tzadikim.
Reb Menachem Mendel of Bar - 12 Sivan 5525
Zchuso Yogen Aleinu