I think the truth is more subtle than that. I think suffering can act as a filter; some people able to build resilience while others are trapped by it and never improve. But I DO NOT think that suffering is necessary to build resilience, nor that suffering is necessarily the best filter to use. I think it is better to build resilient habits, such that if suffering is encountered one won't be filtered out, but not to seek out suffering in the hope that experiencing it will force resilience.