system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] If "size matters not" to force-wielders, what stops a jedi or sith from manipulating large star ships, or even entire fleets?

I've always been confused on why this never happens in the movies, or what the extent of the power of the force really is. The only place I've ever seen this in Star Wars is in the Force Unleashed games, and I don't think that's exactly canon. Is there more in EU on this?
gpt
It's more a lesson than a fact. What Yoda is saying to Luke is that you shouldn't judge a feat by its size. Therefore, assuming Yoda to be a weak Jedi because he is small, or saying that lifting an X-wing is difficult because it is large is what limits the Jedi's mind and makes them weaker than they could be. 

There *are* limits to a Jedi's power - which is why Yoda tells Obi-Wan that he is not strong enough to defeat Sidious. Obi-Wan would not be able to defeat Sidious but if he believed that he could not defeat a Sith Master, he would be even weaker. For a Jedi to attain their full strength in the Force they must be utterly devoted to the concept that they can do anything through the Force.