somebody mentioned passion ?
This is the reason that ANY vocation is not just a job, it shows in the way you approach every flight, every crew, every working day.
Then there are the folks who believe that having spent their 100K the aviation world somehow owes them a living .. some justify their position by their presence , it is easy enough to see potential and part of the task from the left seat is to nurture that through good example and encouragment, others .. bluntly do not which is where the whole PTF thing raises it's ugly head yet again.
The years spent mugging church mice to suppliment the megre earnings of an instructor are actually years well spent: getting out of bed at some godforsaken hour with no guarantee of earning anything leads one to question ones motivation on the one hand and explore alternatives on the other.
If you are still in the frame when it comes to an airline position, you have probably approached every one of those days with dedication and well based optimism that the goal set for yourself is one worth achieving, as you are living the experience, and learning from it.
To echo sentiments previously expressed, I will cease commercial flying on grounds of medical or competence issues only and continue teaching / examining / and hopefully inspiring those with the passion to follow the path I have chosen for myself, having been inspired by others.
Viewing the "experience" in the left seat as an obstacle rather than an asset in ones development does not resonate with me: there were good captains who I learnt from, and not so good captains who I also learnt from, my objective was to adopt the good stuff, and mitigate the bad .. when a command came my way I felt properly prepared rather than entitled.
The term retirement is not one I recognise, that is not to say I will stick with the airline industry past 60 years of age !!