That is a given thing with gambling. We have to accept that as a reality that we'll lose money eventually.
But if you're up for it and taking time in learning how to win them back, it'll also have to cost something for it.
And that's what we need to do, play and gamble in moderation and so our budgets wouldn't be cut for something else and an important matter that we have to address instead of gambling.
Yes, that is a mentality that must be possessed by a gambler, as you said that from the start we must be ready to lose and that is the reason why it is always recommended to only bet with an amount that you can afford to lose, there are many benefits of that mentality, first it can prevent us from excessive emotions that can lead us to various actions beyond control, second our mental and psychological will remain awake, actually everything is interrelated.
Another thing is really not easy to reach the recovery phase or return something that has been lost, remember that gambling is based on probability (possibility) meaning nothing is certain and there is no guarantee either, and that is the reason why a gambler must always apply limits, not only on the amount of money wagered but also on your expectations of winning, as you said, namely gambling reasonably.
We are making it sound easy to recover but you're actually right.
The phase of recovery isn't as easy as what we say. But the encouragement remains there and if someone is on a verge of losing a lot.
And they're able to read it, that will encourage them to do better and recover with enthusiasm.