I think that it is not about thinking too far ahead - as this can only be speculative - but seizing opportunities for growth and advancement in an area that fascinates you at that time - which as the old saying goes means that you never have to "work" another day in your life.
It is about making the most of what is directly in-front of you right now - be that A level choices, degree choices, first job choices, developing skills sets, second job choices, changing direction, going self employed etc.
Nearly 30 years after uni I have seen the need for myself and others to adapt regularly at the right time to the economic climate, to specific issues within a large organisation, to changes in technology and regulations, to our changing personal work/life balance needs (single, in a relationship, working parent, working abroad, children leaving home - the prospect of having to work til you are 80!!).
And the capabilities you need for this are not rigid academic qualifications and employers know this - as they need these too for their businesses to survive.
To the PP above who said that her most successful child was the one that was happiest .... absolutely.
I have done the whole dog eat dog, working round the clock on crazy deadlines under enormous pressure (for too long) and although it is seen as some sort of right of passage in the corporate world - it is also on reflection inhumane and has impacted my family and MH at times. Not sure I will be encouraging my children to go this route - I would feel like I was knowingly sending them up a chimney!!