The mashpiah Michoel Beliner told his friends the dire situation: the doctors gave his son hours to live, and they could not do anything about it. His friends urged him to go to the Tzemach Tzedek. Reb Michoel said, “By the time I get there, it will be too late.”
An elder chossid told him, “The Gemara says never to lose hope in Hashem’s mercy! If you start going, the Beis Din Shel Ma’alah will wait for a limud zechus.” Reb Michoel went.
“When I came in to see the Rebbe,” Reb Michoel related, “and I handed over the pidyon for my son, I was overcome with the thought ‘Who knows what’s doing with my son?’ and began to cry.”
The Rebbe read my note, and he said to me, ‘Don’t cry! TRACHT GUT VET ZEIN GUT.’
“I took these words to heart and did not let any negative thoughts intrude the entire way back. When I got home, I found out that at that moment that I was by the Rebbe, things turned around for my son, and I came home to a live child, Baruch Hashem.”
==== Tzemach Tedek, 3rd Chabad Rebbe
The Rebbe made this saying famous and said that the zechus of thinking positively, exercising bitachon in Hashem that it will be good, makes things turn out well, something that you can see with your own eyes.
UFARATZTA RABBI SHALOM BER MUNITZ