This quote means that the difficult or challenging experiences that you go through in life are the ones that can lead to personal growth and development. These "breakdown" moments can be painful and hard to endure, but they also provide an opportunity to learn from the experience and become stronger and wiser as a result.
By facing and overcoming difficult situations, you can develop resilience, self-awareness, and a better understanding of your own values and priorities. These are qualities that can help you navigate future challenges and achieve success in your personal and professional life.
In essence, the quote suggests that instead of avoiding or fearing difficult days, we should embrace them as opportunities to learn and grow, and to ultimately become stronger versions of ourselves.