The saying “Whatever does not kill you makes you stronger” may be wrong and misleading. Events or people that may kill us or come near to killing us are, by their nature, stressful.
Repeated stress is cumulative, as you may be interested to read in a book by Dutch psychiatrist Bessel Van Der Kolk, MD called “The Body Keeps The Score”.
Using the saying above as a way of coping with stressful events in particular and life in general, requires the use of intellectual effort in order to deny feelings in response to stress. Denial is an effective defense only in very special circumstances and has the bad habit of breaking down over time. Therefore, stress being cumulative and our bodies keeping count of it, think twice about following the saying above as a way of life or as a coping style.