If you want to get stronger and have big muscles, you have to lift heavy weights. And "heavy" here is relative: more than you're comfortable with lifting.
Essentially you're making your leg or chest or arm muscles do something they don't feel like doing (because they've never done it) and in turn you grow stronger and your muscles grow.
Emotions are a muscle the same way.
Deal with situations that you may not necessarily feel like dealing with (but need to), doing stuff you don't feel like doing, the muscles get stronger and grow. Next time that same situation happens (maybe it'll take several times, like a lifting plateau or failing on the last rep), you'll get through it more easily and you can lift more weight, so to speak.
Make it a habit. The same way you don't lift weights once in awhile if you want lasting results, you have to push yourself to do what you need to do often enough to make the abnormal turn normal.
Shortcut for Gains: instead of doing all those reps of lighter weight, do fewer reps of much heavier weight (bigger emotional/mental challenges) -- more results in less time.