What motivated Mr. Smith to carry on?

During the course of The Way Back, when the company is traveling through the Gobi Desert Mr. Smith seems reluctant and unable to go on and is about to give up and die (maybe also in part because of Irena's death, to whom he developed some kind of fatherly sympathy). But one night Janusz talks to him:

Mr. Smith: Just leave me here. You can't, can you?
Janusz: Mister, you know I may not even know your first name, but I...I know your son's name.
Mr. Smith: Irena told you.
Janusz: Yes. Can I say his name?...David.
Mr. Smith: Saying his name won't bring him back. What are you trying to do? Give me the will to live, is that it? Stop me from giving up?
Janusz: And are you giving up?
Mr. Smith: In the camp some thought death is freedom.
Janusz: Why didn't you just kill yourself?
Mr. Smith: Survival was a kind of protest, and being alive was my punishment.
Janusz: Punishment for what?
Mr. Smith: I brought David to Russia.
Janusz: And now no-one can forgive you...and you can't forgive yourself.
Mr. Smith: Irena told me that they tortured your wife and she informed on you...They did the same thing to my boy. Then shot him in the head.
Janusz: My wife is alive. She lived and was released, that much I know. But she'll never be able to forgive herself for what she's done. You see, only I can do that. She will be torturing herself just like you. So you see I have to get back. I have to get back!

After this the next moring he is ready to move on and filled with new motivation it seems (and carries on till the end, or till Tibet at least). But I wonder what really convinced him to go on. Janusz's story about his wife could also have had the contrary effect of giving Mr. Smith peace and redeeming him of his punishment through survival, yet this wasn't the case. But his son was still dead and he had no place to go, which is again clarified in Tibet when he is planning to get smuggled out to the U.S. over China, which isn't really his "home" though and the ultimate goal of his journey:

Zoran: What are you going to do Mister, when you go back home?
Mr. Smith: "Home"?
Zoran: Build metros?
Mr. Smith: I drift a while.

Or was he merely impressed by Janusz's story/motivation and didn't want to leave him alone? What really was it that convinced him to carry on with life and with their exhausting journey? (While it may very well be that there wasn't much more to it than a motivating speech by Janusz, I'd still like to know if there is anything more to make out of his character and his motivation to carry on.)

Best Answer

The shooting script adds some insight into this.

The following description appears immediately after the lines you mentioned:

199 CONTINUED: ( 3) 199

This last, has impressed SMITH, and despite his death- wish a flicker of life surges through his bones.

200 EXT. CAMPSITE, MUD-FLAT - DAWN 200

Next morning, and the figures of the four men are seen in wide-shot sleeping by the embers of their fire. One figure gets up, picks up his staff, and begins to walk slowly South, toward the distant mountains. It's SMITH. The others stir, their attention caught by the sight of SMITH staggering onward. JANUSZ knows what the effort to walk is costing him, and he knows this is SMITH's gift to him. They hurriedly pack up, VOSS cramming the back-pack with roasted snake-meat, ZORAN collecting a last bowl of water, which he pours carefully into their goatskin water-bag.

So the implication is that Janusz's story has motivated Mister to continue on, not for himself but for Janusz. I think he realizes what his death might do to Janusz and he decides to survive in order to help Janusz survive and reach his wife again.

Remember also the following lines which are not in the shooting script but are in the movie and appear right before the dialog in question.

Mister: It can kill you remember?
Janusz: What?
Mister: Kindness. Just leave me here. You can't can you?

I think Mister realizes that Janusz is willing to do anything he can to help Mister survive and that if he gives up he is putting Janusz's life at risk as well. So he decides to push on and live for the sake of Janusz not having to lingering to help him as he gives up and dies.