What do we learn from "Tocheles Memushachah Machalah Lev"?
Brachos 32b: Anyone who prays at length and anticipates that it will be answered will come to heartache 1 .
Rashi: If one promises to his friend and does not fulfill, this brings heart illness. Here, "Machalah" is not a noun, like it is in "va'Hasirosi Machalah mi'Kirbecha" (Shemos 23:25). Rather, it is a verb, like "Ma'ale Gerah" (Vayikra 11:4).
Malbim: Tikvah applies to something that there is no promise that it will surely come. Tocheles is something that was promised; he is sure that it will come. Mis'aveh does not have even Tikvah; he merely desires, without hope of getting it. Also Tocheles, if it is prolonged and does not come soon, only later, it already makes the heart ill, even though he is sure that it will come. All the more so, a heart that is Mis'aveh will be ill! This has no cure - "Ta'avas Atzel Temisenu" (21:25). If it does come, even though he did not hope for it, it is like a tree of life. It revives his Nefesh that is Mis'aveh.
32b, 55a: The remedy is to engage in Torah -- "v'Etz Chayim Ta'avah Va'ah", i.e. Torah - "Etz Chayim Hi la'Machazikim Bah." If one prays at length without anticipating results, it will have an effect. If he expects to be answered, this arouses mention of his sins (and causes that he not be answered).
Why does it say "v'Etz Chayim Ta'avah Va'ah"?
Rashi: The verse should be re-arranged. When desire comes, it is a tree of life. The hope that Hashem put in Yisrael, and made them anticipate returning, and they did not return, in the end, they had heart illness. When His desire will come, that they will do His will, it will be a tree of life for them.
Malbim: Refer to 13:12:1:3.
