The Abarbanel explains that a person can be extremely wealthy but as long as he isn't happy with his lot he will never be considered wealthy. Conversely a person can have very little but if he is happy with his lot then he is wealthy. He explains the reason for this is that in regards to any other desire in the world once the desire is met a person doesn't want any more. If he is hungry and eats a lot then when he is done he no longer desires food. If he is tired and he sleeps a lot he can't sleep anymore. With wealth though a person's body doesn't reject more money "as there is always room for more". The desire can never be met in this regard. Therefore the only way for a person to feel fulfilled in this aspect is if he is happy with the lot he has attained.