Messing with time has large repercussions.
First of all, changing the past shouldn't be possible. The first major problem is that alternating a timeline produces another timeline.
Say, a boy is born in the year 2000. In 2020, he turns twenty. He realizes that his grandfather left him a time machine. He decides to go back in the past and meet his grandfather.
When the boy's grandfather realizes that the boy used a time machine that he made, the grandfather will try his best to build a time machine. Before meeting the boy, the thought of building a time machine might not have crossed his mind
Though time is not absolute, there are some major incidents that must happen to keep the balance of the world.
The boy had to use the time machine and meet his grandfather to inspire his grandfather. If the boy and the grandfather hadn't met, the grandfather might not have built the time machine.
