Is it fair to expect someone who's been broken to act as if they haven't been?

So this is my first post on here because i literally need someone to give me a different take on my question. it may seem like im just venting, but i do think of this often no matter how things going for me in life.

to the topic, we all now how every thing that happens to you in life is then redefines your outlook on everything, some do more some do less. so for example there are 2 people, each one is lighthearted, kind and full of life, then they meet their first love, first one meets an amazing partner who is their true love, they have ups and downs but in general they're more than good. the second one falls in love deeply but gets his soul shattered by SO, which changes his mindset and perspective, this person just will never see the logic to show same amount of kindness and cheery spirit as he used to.

many people say, dont let the pain make you hate, dont let the world make you hard. let's imagine both of these people had not easy lives till the moment they met their SO, yet managed to keep their warmth, but then this moment sends their lives in opposite trajectories, so how does this work, why some people get the boost for keeping warmth in their heart while others get beaten down, and then we judge those behaviours equally? he didnt ask to be broken and now just simply protects himself, should he really go against his instincts and logic if he knows there's huge possibility to be out of luck once again? is this the point of life—to keep playing Russian roulette with your heart?