Mountains
A bit like climbing a mountain I would imagine, the key to success is careful preparation and planning, physical fitness and a degree of luck. It doesn't matter about "being in your blood", or "sacrifices" or "faith" or "dreams" or other flowery nonsense. Save that for the biography.
The reality is that there are boys and girls sitting at their school desks at this moment who may never have given a flying career a second thought, who in 5-10 years time will be flogging their way back and forth to airports around the globe, as part of their daily professional lives. Similarly there will be people who decide at an earlier or later stage of their lives that this is a career they want and feel able to embark upon.
Firstly, there is a medical standard, and although there is some fluidity in this regard, if an individual cannot obtain certification, then further progress is practically barred to them.
Secondly, there is the research. Understanding the reality and nature of the career they are seeking to embark upon. Within this phase lies such things as experiencing flight, determining what qualifications will be required. Assessing the risk for themselves (financial, ambition, other career options, time requirements, fall back options, contingencies, etc.)
Thirdly, there is the planning phase. Raising the necessary finance, seeking out the best training, having financial contingencies arranged, arranging "base camps" and safety "caves" where you can stop and take shelter if and likely when circumstances start to work against you. Finding people who can assist and support where possible. Assessing a sense of self awareness, so that you can maintain the requisite levels of determination, flexibility, adaptability, common sense, and preservation. The most sensible will always leave themselves with an escape route.
Forthly, There is the expedition itself, where all the preparation and planning is put into practice. It is here that success or failure will depend on how how much effort went into those prerequisites as well as a significant element of luck. Setbacks will not be unusual and many people will fall by the wayside, either permanently or to try at a later point in time. It is certainly true that (of those who succeed) some individuals will take longer to reach their eventual goal than others. The reality at this stage is that those who were poorly prepared and equipped or adaptable or unlucky, will fail no matter what their "dream" or what "was in their blood".
Fifthly, success and achieving any ambition is the reward or high. Whatever the climate or however long it might or might not take, there will be a proportion of those who started out, who will make it through. Of course it is at this level that having achieved the goal, reality starts to set in. Hopefully the earlier research will have prepared the individual for the career they have embarked upon, but it is now that the career really starts, and often it is a lot more mundane than the more exciting phase of achieving the opportunity. The prospects at this point are like many other careers. They include advancing your position through further education and experience. Maintaining your employment and your professional standards. Having the resources of your employment to get on with other aspects of your life.
It is certainly true that there will also be rare individuals for whom luck will allow them to survive poor planning and preparation when others don't. Conversely there will be those who are rich enough to have a helicopter to take them to the top of the mountain. However for the 99% of other wannabees this is the reality.