Building strength in any area works in the same way. Consider muscular strength. Ask a bodybuilder and they will tell you it is after the exercise routine that they build new muscle. New muscle is created when the muscle fiber ruptures and the nerve fibers begin to register pain. Pushing yourself at that precise point makes all the difference. Within 48 hours, your body compensates for the damaged fibers, and the muscle is rebuilt with added strength.
The same principle works with emotional strength. Resilience, patience, awareness, enjoyment, and other virtues all become stronger when we push ourselves to the limit and stop right before the breaking point. When you exercise an emotion beyond its normal limits, the practice gives you more control the next time that emotion arises.
For instance, when your patience is tested to its limit yet you persevere and maintain your composure, you enhance your patience moving forward. The next time you find yourself in a situation with an overwhelming amount of information (on a busy city street, in an airport, at an antique mall), challenge yourself to fight through the noise and maintain your focus. In doing so, you are actually building the emotional reserves to become more focused in the future. How cool is that? Time for a workout!