It's called hormesis. Yes, there is a range beyond which further stress causes permanent and serious damage, but within the hormetic range "adversity" is basically the proximate cause of growth.
According to Sapolsky's lecture on depression [1], a stressful childhood experience is 30x more likely to cause depression in individuals with a particular serotonin-related gene variant.
[1] https://www.youtube.com/watch?v=NOAgplgTxfc @ 47:00
No. [1] The context of the whole conversation is traumatic relationships. If anything you are talking about eustress - and traumatic relationships are not beneficial and do not "make you stronger" [2].
[1] https://en.wikipedia.org/wiki/Hormesis
[2] https://en.wikipedia.org/wiki/Eustress#Compared_with_distres...