The theme of the film is to trust your convictions, even when everyone says they are impossible.
We can arrive at this answer because:
"Smallfoot," tells the story of Migo and Percy Patterson.
Migo is a yeti, who lives in an isolated alley. He faithfully believes that human beings exist, yet everyone around him thinks otherwise and judges his conviction.
Percy Patterson is a filmmaker who can't get an audience for his work, but he believes he'll make it sooner or later. However, the people around him do not agree and laugh at his failure.
The two characters end up meeting and helping each other achieve their goals. In this case, we can see that the theme of the film is related to the confidence we have in our convictions and this is related to our dreams and goals.
