How would you know the person is 'better'

We put our best foot forward when we meet someone, so while they may appear better at the moment, it could change over time.

In fact, that is why men and women will typically 'test' the waters with a new love interest before breaking it off with their current significant other.

They may cheat in the process or just have enough indicators that they are ready to move on to someone else.

Think of it like a monkey swinging from branch to branch. It won't make the leap onto the next branch, until the monkey senses that it is safe to do so.