Once upon a time, there was a very smart scientist named Professor Smith. He was very good at inventing things and loved to explore new ideas. One day, he had a brilliant idea to create a time machine. He worked very hard and finally, he was able to build it.

The time machine was a big, shiny machine with lots of buttons and levers. Professor Smith was very excited to try it out. He set the date to go back in time to the year 1900. As soon as he pressed the button, the machine started to shake and make loud noises. Suddenly, he found himself in the year 1900!

Professor Smith was amazed by what he saw. He saw people wearing old-fashioned clothes and riding horses instead of cars. He explored the city and even met some famous people from history. He was having so much fun that he didn't realize the time was passing by quickly.

But then, he remembered the reason why he built the time machine. He wanted to change some things in the past to make the present and future better. So, he went back to the present time and was shocked by what he saw. Everything was different and not in a good way.

The streets were dirty, the air was polluted, and people were not happy. Professor Smith realized that every action he took in the past had a big impact on the present and future. He felt sad and guilty for causing all these problems.

He decided to go back in time again and fix everything he had changed. He went back to the year 1900 and made sure to not change anything this time. He just enjoyed his time there and then went back to the present.

To his relief, everything was back to normal. The streets were clean, the air was fresh, and people were happy. Professor Smith learned a valuable lesson that day. He learned that sometimes, it's better to leave things the way they are and not try to change the past. From that day on, he never used the time machine again and focused on inventing things that would make the present and future better in a different way.

The end.