Near the end of our Parsha, we read:
“And the hands of Moshe were heavy and they took a rock and placed it under him and he sat on it. Aaron and Chur supported his hands, one on either side, and his hands remained an expression of trust until sunset.” (Sefer Sh’mos, Perek 17, posuk 12)
Rabbi Pliskin in Growth Through Torah cites a Rashi which states;
“…Moshe did not sit on a comfortable pillow, but a rock. There was a battle going on with Amalek and Moshe wanted to feel the suffering of the people. This, said Rabbi Yeruchem Levovitz, is a lesson in feeling for another person’s suffering. Not only should we mentally feel their pain, but it is proper to do some action in order to feel some of the discomfort yourself when someone else experiences pain. This way [through empathy] you actually feel his pain.” (Growth Through Torah, Rabbi Zelig Pliskin, page 177, citing from Daas Torah, page 152)