Sometimes what we call self control is actually the result of opportunity. Your sister tried but she may have had an opportunity that not everyone else has. Many people in the same situation can't take risks even if they want to, because they are afraid that if they fail, their family won't survive, So I think not only desire, but also time, opportunity and mental preparation play a big role.
And I conclude that if we have a belief that has a positive goal or can lead to something better, then it is not wrong to do it, even if it is said to be risky, it is not a bad thing. That is what I conclude from my sister's case.
But in this case, of course, what you have lost is true. Mental strength is indeed quite important and plays a significant role, because achieving results that can make us sufficiently satisfied is certainly not easy. There will be obstacles that arise, and this is where mental strength is tested.
I think in your sister case, we can conclude that environment only present collection of probability such as job opportunity, wages, living cost, education & health access, sucurity and social guarantee, the result from processing opportunity choice is depend on each personal character. But what we often forget, environtment give big influence on how we describe "a normal life", how we define success & fail, pressure tolerance level and decision making pattern. Example, in consumtive environtment, debt is something normal, overshopping is previledge not showing bad financial literacy. Strong personal character and internal system can protect us from environment bad influence, system mean good habit not temporary motivation, when we have good habit, we have our own value and not normalize something bad in our environment common practice. Not all local norm is healthy and not all social habit, we must follow. Its mean we have control in our life without avoid our environment.