The kicker, for me, is the prioritisation between happiness now and happiness later.

To give an example, I live fairly frugally life and stick ~20% of my salary into a pension. But a friend has invited me to their wedding across the Atlantic. That's a couple of thousand pounds right there.

Let's call it £5k after flights, food, hotel, etc.

£5k @ 5% interest for 25 years is ~£17k.

Is seeing a friend get married to the love of his life worth seventeen frickin' grand?

That's lens through which you have to view every financial decision when you're on a savings plan like this. Not how much it costs you now - but how much it will cost you in the long run.

(PS - the answer is unequivocally yes. Totally worth it for me. YMMV).