Faith can be considered a weak thing unless it is tested. Think of it as a muscle. It gains strength only when pushed by exercise. The harder and more regular the exercise the stronger our muscles become. As humans, people are weak in themselves. It's easy to take God's favor for granted, to get used to it and lose some of that consciousness of the excellent provisions God provides for our care. We can forget sometimes that we are God's lilies and become thorns without realizing it.
The true strength of one's faith can not be seen in the contented status quo. Faith is tested and tried through hardship. It is easy to give thanks and praise for the many good things we have when life is stable and our circumstances pleasant, but during hardship we often focus entirely on the immediate difficulty, losing the ability to look at the broader perspective and see the present more as Christ might see it. Without hardship, we would not get to see the glory of God in enduring or overcoming adversity. Difficulty allows us to see how powerful God truly is.
When we persevere in difficult times, keeping a positive attitude and remembering to give God the credit and our gratitude for bringing us through it, we achieve victory. In 1709 John Wesley's father Samuel called all the neighbors together as his family's house was burning to the ground to say a grateful prayer that all the family made it out alive. When I stop to appreciate what I haven't suffered, the sufferings I do face lose their sting. The exercise can put an abrupt end to a bad attitude. Even the small irritations could be blessings in disguise.