The Myth of 'Size Matters Not'
Yoda famously claimed that 'Size matters not,' but Star Wars has proved he was completely wrong. The Star Wars franchise is always growing and evolving, and that naturally means there have been a massive number of Star Wars retcons. With the amount of content that has been produced in the 46 years since the first Star Wars movie hit theaters, there will inevitably be inconsistencies in canon.
Yoda Uses the Force Star Wars Empire Strikes Back.
With so many things to keep track of, it can hardly be expected that every Star Wars writer and director would be able to read/watch all of them. Surprisingly, though, even Yoda's most famous line - advice straight from the Jedi Grandmaster - has effectively been retconned. In The Empire Strikes Back, an exhausted Luke is challenged by Master Yoda to lift Luke's sunken X-Wing out of the swamp. After trying and failing to do this, Luke complains to Master Yoda that his request to lift the ship out of the swamp is unreasonable. Luke argues that such a feat is impossible. In response, Yoda says perhaps his most famous line: 'Size matters not!' Luke does not accept this answer, but he goes off into the brush to sulk after refusing to try again. A disappointed Yoda then proves Luke wrong by using the Force to lift the ship out of the mire himself. His action seems categorical - and yet, it was wrong.
Obi-Wan and Yoda on Dagobah Empire Strikes Back
The Force Can Drain An Individual User’s Energy
Since The Empire Strikes Back came out, it has been consistently proven that the Force drains the user's energy. For example, in the Star Wars: The Clone Wars TV show, it takes a few Jedi to break into Cad Bane's mind. Because his mind is strong, it is too much effort for only one Jedi to manipulate it. That's only a minor example, and explainable given the possibility Cad Bane has a stronger mind than a Jedi. But perhaps the best example of this principle is in Star Wars: The Last Jedi when Luke uses the Force to astral project to fight Kylo Ren and apologize for what he did to his nephew. The effort that this takes kills him. Clearly, using the Force is no small feat.
Luke teaches Rey about the Force in Star Wars The Last Jedi.
This is also confirmed in Charles Soule's Light Of The Jedi, set during the High Republic Era. There, Jedi Master Avar Kriss performs a Force Meld that embraces all the Jedi in the galaxy so they can use the Force to save a star system from destruction when a canister of liquid Tibanna approaches the sun at near-lightspeed. No one Jedi could do this alone, and the combined effort led to several Jedi dying while they struggled to save the star-system.
Yoda and Darth Vader using the Force in Star Wars.
The same is proved during the Star Wars prequel trilogy. When Obi-Wan is about to be crushed by a pillar, he needs Yoda to save him. Lifting something that large made out of metal is too much for him. Further, it is clear that it takes a huge amount of physical effort for Yoda to do so. Count Dooku gets away specifically because Yoda cannot rescue Obi-Wan and fight him at the same time. Therefore, the idea that size doesn't matter at all is nonsensical. There is a big difference between lifting a feather or a piece of an apple with the Force and something large like a pillar or X-Wing.
Grogu, DIn Djarin, and Luke Skywalker.
The Force Still Has To Work Around Physics
The energy that it takes isn't the only problem with the idea that size doesn't matter when it comes to the Force. In The Anatomy Of A Space Western: The Science Of The Mandalorian, Mark Brake points out that the Force has to fight against inertia and gravity. He notes that Jedi (and potentially other Force-sensitives) likely fought against the gravitational forces of Tython to arrange the orthostat stones in the order shown in The Mandalorian chapter 14. He also makes the observation that in Obi-Wan Kenobi, an out-of-practice Obi-Wan struggles to lift the relatively light 10-year-old Leia Organa with the Force.
Yoda on Dagobah
The forces of inertia and gravity are a big factor when it comes to using the Force. After all, the more things that an individual has to fight against, the more effort that it takes to move something. In Timothy Zahn's non-canon novel Outbound Flight, Obi-Wan Kenobi and Anakin Skywalker try to stop a flying missile. Neither of them can do it. The inertia is too strong for them to hold it back. Jedi Master Jorus C'baoth stops it, but only because he is extremely strong in the Force. Even Obi-Wan and a young Anakin Skywalker - two skilled Jedi who are powerful in the Force - are not able to stop something in motion.
Lower Decks structure looks like Yoda's home on Dagobah
The Importance of Physical Training for the Force
This explains why the Force requires intensive physical training. When Yoda is training Luke in The Empire Strikes Back, he makes Luke do physical exercises, such as running with the weight of Yoda on his back through the swamp. This isn't just to make Luke better at fighting in a lightsaber duel. The Force itself requires both mental and physical stamina. If an individual Force-user wants to become strong enough to move large objects - such as an X-wing that is being weighed down by water and pushed downward by gravity - they need to have the energy to withstand the physical toll that takes.
Yoda trains Luke Skywalker on Dagobah
Luke cannot lift the X-Wing right away, not because he doesn't have a strong connection to the Force, but because he doesn't yet have the physical strength to perform such a feat. Yoda posits that Luke cannot do it because he has no faith in himself, but this is not entirely true. While Luke's attitude was limiting him, the exhaustion he was feeling was real. Yoda had been building up his stamina and strength for almost a thousand years. Further, upon examining the scene closely, it is clear that even Yoda felt the strain of fighting against gravity to lift something so heavy. As it turns out, size does matter, whatever Yoda's famous Star Wars advice may have been.
