You sure about that ? And how big ? Big means big renewal fees. They have to be offset by sales revenue.
Domainers all think they have outstanding names and they are very often infatuated with their portfolio. But it's up to the end users to judge.
At least 99% of registered names have no resale value anyway, and will never sell.
If you have great names, then you should receive inquiries and unsolicited offers from time to time. If you never received any in 10 years, then your names suck or are just too niche to sell.
I think you're talking about A Rosener.
But indeed, I would guess the majority of successful domainers have lost money in the beginning. You have to learn from your mistakes, the sooner the better.
So if you lose money in the first year, it doesn't mean you will never be a good domainer. You have to learn from your mistakes (and the mistakes of others), you have to learn what kinds of names end users want, and then acquire the right type of inventory. Inventory is what drives sales.
Everything else is details.