The Rebbe's guidance on the inner struggle between the G-dly soul and the animal soul — the yetzer hara and how to face it:
The struggle is part of the plan. Inner struggle is part of G-d's design for our growth; face it with joy rather than distress (IK 3836). Struggling with the yetzer hara is normal and expected (IK 2574), and setbacks are normal too — ultimate victory is certain (IK 3354, 8320). Every Jew has two souls, a G-dly soul and an animal soul (IK 8553); true inner peace comes when the G-dly soul prevails (IK 740, 1479). Even after sin, one can reach the level of a beinoni or even a tzaddik (IK 3306).
Recognize its tactics. Doubts or arguments that weaken one's positive actions do not come from the yetzer tov (IK 3200). Discouragement, despair, sadness and feelings of inadequacy are tactics of the yetzer hara (IK 3167, 3295, 3486, 3813, 5011, 6325, 6648). So are excuses for leaving Torah study or avoiding Chassidus, blaming others, and doubts about one's environment or path (IK 2652, 2973, 3775, 6895, 8006). It tries to frighten (IK 2656, 10950), and to stop someone precisely when he is thriving (IK 2894, 2933). Confront it with inner strength, and never flatter evil (IK 2400).
How to overcome it. All struggles come from one source and can be overcome by strengthening Torah study and positive influence on others (IK 2756, 6482). Guidance for distinguishing the yetzer tov from the yetzer hara is found in Tanya (IK 5519); learning Tanya passages by heart helps (IK 6711). Divert your mind from negative thoughts rather than fight them head-on (IK 5070). Serve G-d by refining the animal soul, not by afflicting the body (IK 2908, 4196), and elevate the animal soul through avodah (IK 1682, 5511). Recognize your strengths as well as your weaknesses (IK 7231, 046). Daily conduct and a supportive community help (IK 7720).
See also: Emotional well-being – Self-confidence and feelings of failure; Torah study – Motivation, diligence and study partners; Teshuvah – How to do teshuvah.