We're going to have to face, for possibly a very long time, a big drop in salary. We might have to move back home, it will be hard to sound impressive at parties about what we're doing, and we'll be beginning again close to zero.

Tellingly, the agony about this can be most potent when we're young.

Imagine someone who's 20. They've been planning a career in chemical engineering and they're well on the way to gaining the right qualifications.

They selected particular subjects at school, took the right courses at university, and did some relevant work experience.

They've already made what feels like an enormous investment.

But now, they start to think very seriously of switching course, perhaps towards marine biology or anthropology.

It might mean another two unforeseen years of studying.

At 20, two years feels like a very long time indeed: 10% of the whole of one's life so far.

And psychologically, it's even bigger than that.

At 20, you've maybe only felt you were you since you were about 16. Before that, you were in a kind of daze of childhood and adolescence, and didn't have any real idea of what your life might be about.

So, two years feels like half of your existence.

It's a vast commitment.

What's so hard to grasp, and yet essential, is how things will look in the future.

Age, say, 56.

From there, two years will have a very different meaning.

It'll only be one twentieth or 5% of the forty years between being 16 and being at the climax of middle age.

Over time, the length of further study grows relatively small against the backdrop of a whole working life, while the consequences of not having undertaken it grow ever larger.

We call his paradox the "job investment trap," and it explains why many people, especially young people, mistakenly turn away from retraining.

The present looms too large and the long long future, which will in fact constitute by far the greater part of our lives, doesn't carry the weight it really should.

To counter this tendency, we should draw up timelines to force ourselves to see that the period from 16 to 24 is truly quite short in comparison with what lies between 24 and 65.

We need to weigh up investments now, not against our most recent experiences, but in the light of a more accurate picture of an entire life.

We need to believe in something that's so hard to really trust in: the reality of our own future decades of life.

And then, we need to dare to switch track.