So as price goes up you sell a little but because you are getting more euros per sat your sat balance isn't declining dramatically.
In a very simplistic way of looking at things, if Bitcoin would appreciate at the exact rate as the interest of my loan, I would come out of this whole gamble with 0 profit/loss.
The reality is that volatility is much more wild, and there have been both good and bad times (in terms of having to sell below and above my entry price).
Things are looking good, but only time will tell. There's more than 8 years of future left to see.
In that case you should have a back up plan to be able to cover fiat debt repayment via cash flows.
Yes, if the price stays low enough for long enough, the BTC stack goes away and I'll have to face the remaining debt with my own cashflows. Knowing this, I went for a level of debt that is manageable for my financial situation.