50%

Well, I learned this rather late in life, but it is a very good thing to bank/invest 50% of what you make and learn to live on the other 50%. 

I wish I had made this connection when I was, you know, 14. However, it's not too late even for me (though still a work in project thanks to lockdown), and now I try to tell this to the younger generation. Unfortunately, they so far look dubious or--apparently--even laugh. Tact and timing is needed--and also understanding because the young have little dreamy dreams, and it is sometimes hard for them to understand that although life should be a bed of roses (shouldn't it?), it so rarely is. 

Young People are also averse to the idea of working a difficult job for 10 - 12 years, investing as much of their pay as possible and then retiring at (or before) 34 to do a super-fun, potentially ill-paid job--or start a risky dream-business--as their investments merrily pay their way.  

And, having looked at this from their point of view, I get it. If the teenager is female, she doesn't want to work a difficult job ever, but do something interesting and worthy of her precious youth--like get married and have children ASAP, or go to graduate school and become the next Edith Stein, or write short stories and then novels and become celebrated ...  

I'm sympathetic to this because, let's face it, the years between 20 and 30 (or, post Bachelor's degree, 22 - 32) are way more golden and interesting than the years between, e.g. 40 and 50---are certainly seem so when you are 18, and 40 is SO OLD!

If the teenager enjoys worldly stuff, the idea of living on only 50% of his salary (whatever it is, and it is always smaller than you think, thanks to taxes and other deductions) is going to be terrible. I am less sympathetic to this unless the teenager expects to be very poorly paid indeed. 

If so, why? When I was a teenager (so forgive me), I thought that only the dumb girls would leave school at 16 and study hairdressing, or some other trade. Then in my 20s I met a young salon owner, and she was not dumb at all. She was a good businesswoman, having taken management, etc., classes when her fellow beauticians were partying and saved money towards her own shop. These days I am not as interested in how much cache a job obtained by a young person has but how much they are able to save without becoming unhappy. 

Obviously the best thing of all would be for the Young Person (or the Young Person's Future Husband--although depending on the Young Person's Future Husband is a risk rivalling Bitcoin) to train for/be educated for a field that they will truly enjoy and will actually earn them good money--that is, enough for them to invest 50% without living like Uncle Ebeneezer in Kidnapped.

Sadly I grew up with a lot of expectations that everything would be magically handed to me on a plate (why?) and that I would never need to worry about money, really, because I would marry someone with a job as solid as my Dad's and I could just focus on developing my lovely brain and my precious art. It could actually have happened that way, but as history unfolded, it did not. But I think this "save and invest 50% of everything you ever make" is future-proof, and the difficulty is convincing the very young that this  really will pay off.  

Update: By the way, I too still have little dreamy dreams. The biggest difference between the dreamy dreams of my teenage years and of my middle years is that I now know exactly what steps to make them come true. Well, that is, some of them. Some of my little dreamy dreams involve being able to play with my Godling in Poland and my other Godling and her brothers in Canada and seeing my family in person. These, sadly, depend on various governmental fiats.  However, the COVID-19 pandemic and subsequent lockdowns and restrictions, police beatings and proposed vaccine passports can be used as a Teaching Moment to the young that you never know what is going to happen, and therefore, save 50%.