There were no second chances. People always said that, meaning that once something had happened, it was difficult to undo. There was reason behind it.
Because the vast majority of people had no Time Travel abilities, and even those who did faced many dangers when reversing the past. The most typical example was the Flashpoint phenomenon.
Barry had only wanted to save his mother. What had he done wrong? Yet that single thought had directly created a warped Timeline like the Flashpoint Universe, where Superheroes were no longer heroes and met different destinies.
Sometimes even the slightest change on an alternate Timeline could create tremendous uncertainty in the Future. But if everything was considered carefully, Flashpoint could be avoided.
That was why Batwoman only dared to engage in short-term Time Travel, such as going back to yesterday, the day before, or last week.
The longer the interval, the more factors had to be considered. She could not guarantee that everything would remain within controllable variables.
What did the range of variables mean? It could be explained abstractly, but it could also be simple. Put in easily understood terms, events on a Timeline inherently allowed for slight changes and errors.
For example, if someone wanted a drink of water and you went back in time to secretly move his cup a few centimeters to the left or right, then in most cases, nothing would change. He would still drink the water and achieve the same goal of quenching his thirst.
But if you secretly replaced his water with cola, the variable would be greater. He might not like the drink, or it might not quench his thirst at all, causing him to look for water again and setting off a series of changes.
Then again, there might not necessarily be any