The Rebbe warns against the Yetzer Hara’s tactic of instilling despair over spiritual shortcomings, urging persistence in Torah and mitzvos despite past failures. He encourages strengthening one's resolve, seeking guidance in Chassidus and Tanya, and maintaining daily Tehillim, assuring that with effort, success will come.
https://www.torahrecordings.com/rebbe/igroskodesh/014/004/5011