The following lesson in Likutei Moharan (Tinyana 10) can help us understand why sometimes Yishuv Hadaas is easily attainable, and other times not. We need to identify a key differentiation between happiness and excitement, and also between sadness and depression. When someone is excited, even though it's typically a good-feeling, their mind isn't settled. But when someone is happy, it's a pleasureful calm feeling of contentment and satisfaction, which is a good platform for Yishuv Hadaas. On the other hand depression prevents our minds from settling because, when we are depressed, God forbid, we are have a feeling about our feelings. Sadness alone isn't necessarily the same thing. It can sometimes be healthy to feel sad. It's possible to feel sad and get into Daas. That's the idea of a broken heart, which is beloved by HaShem. But once a person judges themselves for feeling sad or is resentful of their Creator because of those sad feelings, that's when it gets difficult to get back to Daas.
“For in joy, you will go out” (Isaiah 55:12)
The sole reason why people are distant from God and do not draw close to Him is because they do not have a “yishuv hadaas”—[that is,] they fail to settle themselves. It is essential for a person to strive to think clearly about the ultimate purpose of all worldly desires and affairs—both those cravings for pleasures experienced by the body, as well as those cravings for non-physical things such as honor and the like. [If a person can do this,] then he will certainly return to God.
The main way to achieve and maintain a settled mind is by being happy. This is because when a person is happy, he can direct his mind as he wishes, and he can settle his mind to think about the ultimate, eternal purpose of his life. For joy is the realm of freedom, and consequently, when a person binds joy to his mind, his mind is then free and not in exile. Then he can attain a settled mind.
Through depression, however, the faculties of the mind and understanding are in exile and it is difficult for a person to gain the presence of mind to return to God. It emerges, then, that depression is a very great barrier to serving God. When a person is happy, he becomes a “free man” and he leaves his exile, as it is written, “For in joy, you will go out” (Isaiah 55:12). Exile, on the other hand, causes the mind to be unsettled, as our Sages, of blessed memory, said about the Ammonites and the Moabites: “They had presence of mind because they didn’t go into exile, as it is written, ‘Moav enjoyed peace from its youth … it did not go into exile; therefore, it kept its flavor’” (Jeremiah 48:11; Megillah 12b)".