Because it is right

Guided by the merchant and the two guards, the white unicorn entered the town hall and was received by the mayor, surrounded by four counselors and another bunch of guards.

“Could you explain why you interrupt our session?” asked the mayor, angered by the situation.

The merchant, the two guards and Shia stood silent for a bit.

“It’s about the orphanage…” began the merchant.

“Then it doesn’t justify interrupting our session!” sharply replied the mayor.

Shia decided to intervene, as she wasn’t ready to just wait to be received, which she felt could have taken days, days she didn’t have due to her reveal to the guards and the merchant.

“Could you explain why the orphanage doesn’t have enough food for the orphans?” she asked the mayor.

“No.” the mayor replied. “I don’t have to explain anything to you.” he said. “Everything is fine with the orphanage.”

“You lie! I was there, I saw how little they have to eat.” Shia responded.

But the mayor had decided it had gone far enough. He called upon the guards to make those four ponies exit the building by force. But before they could act, Shia’s horn lit up with a yellow magical aura and the spell took away her dress, which allowed the white alicorn to spread her wings wide, and revealed the sun on her flank.

All the guards instantly bowed down to the princess, as did the mayor and his counselors.

“Do you happen to care giving an explanation about the orphanage yet Mayor?” Celestia asked with authority.

The mayor was caring, but certainly didn’t want to give any explanation, as he didn’t have any. At least no good one, none that would prevent having to admit he had kept the tax money for himself.
He looked around to his accomplices, but none of them looked like having any solution. As for the guards, they were all ready to obey any order from the princess.

It was over. But the mayor couldn’t understand why the princess had come to his little town in the middle of nowhere. Why she had suddenly taken any interest in that orphanage and why her mane wasn’t looking like he was told it should.
He was a very well educated and knowledgeable pony. The mane was an important indication, he was certain of it. He had heard of an alicorn mane ceasing to flow and go back to look like a normal mane in one case: when the princess of the night, Luna, had just created the moon which had depleted her from most of her powers.

That was it. He wasn’t certain, but it was worth trying, so he shouted:

“This isn’t the princess of the sun!”

The guards frowned and looked hostile, as they could clearly see Celestia was an alicorn and had the royal cutie mark on her flank.

“Don’t let that impostor fool you.” the mayor kept yelling. “Ask yourself! Why would the princess of the sun come here to take care of an orphanage while there are so many more urgent matters to take care of in Canterlot!”

Some guards thought about it and agreed that it was, indeed, weird.

“Tell me why, if this mare is the real Celestia, her mane isn’t flowing? Why she has dirt on her hooves, why she would have come without any escort or any announcement!”

Now, all the guards were wondering about those questions. They had to admit it was all very strange.

“Look at the dress she was wearing!” the mayor continued. “Does it look like the dress of a princess?”

He knew he hadn’t convinced the guards. At least not completely. He had just created enough of a doubt he had to exploit. After all, Celestia was still an alicorn and that fact alone would be sufficient to overcome him overtime. At least very probably. So he took his chance and added:

“You want a real proof? Have her control the sun!” he shouted.

All the guards turned their attention to Celestia whose expression had turned from victorious to horrified.
The mayor’s plan was working beyond his wildest dreams.

“So, what about it? All you have to do is make the sun set and rise to clear any doubt about your identity.”

Celestia froze completely. She had lost. In a matter of seconds, she had completely lost. In a vain effort, she tried to accomplish a miracle and called upon her alicorn magic. The room filled up with energy, electrifying the manes of all the ponies there, and all looks turned to the windows and the sky behind them with the sun dominating it all. But it didn’t disappear behind the horizon. It didn’t move at all in fact. Celestia’s concentration broke and she fell on the floor, exhausted.

The mayor exulted!

“You see! She is not the princess of the sun. She isn’t a princess at all. She is nothing but an impostor!” he said in triumph.

“Please…” Celestia implored. “Don’t listen to me because I am supposed to move the sun. Listen to me because what I say is right.”

“Throw her in prison!” ordered the mayor.

The guards hesitated, still unsure, but as Celestia was on the floor, proven unable to influence the sun, and the mayor was standing up, clearly in power, they slowly began to obey.

And just at that moment, Foster entered the town hall with a bowl of water.

“Wait! Wait!” he shouted. “I’ve got it. I’ve got the soup!”

He went in front of Celestia, who achieved to sit, and put the bowl of water at her hooves.

“What is it?” the princess asked.

“My special super duber awesome soup!” replied Foster with a smile.

Celestia looked at the bowl, then at Foster, then at all the guards around who had no idea anymore how to react.

“What are you doing?” she asked the stallion.

“I’m fulfilling my promise. Here is the soup.” he replied.

“It’s just water.” she said.

“Yes, I know. I couldn’t decide what kind of soup to make and it doesn’t really matter anyway. It was only supposed to be sort of a symbolic thing, you know, to make you realize you had the strength inside of you the whole time?” Foster explained with a genuine smile.

Celestia looked at the weird stallion with both happiness and despair. Happiness because he was looking so joyful, so genuine, so simply happy that it was contagious. Despair because he was utterly useless.

“Oh, I know!” Foster said.

And he put some leaves into the bowl of water.

“Could you heat it please?” he asked Celestia.

The princess sighed and used her magic to heat the water under the eyes of all the ponies that were there, waiting to know what was going to happen.

“And now?” asked Celestia, as the water was warm enough, at least in her opinion.

“Now that tea is read, we drink it.” Foster replied. “But we might have to do it somewhere else.” he added.

Celestia understood and sighed, as the guards, having finally realized nothing was going to happen, took both the princess and the weird stallion into a cell, with a lot of respect, so much in fact that they made sure to bring the tea too.