My ex moved on so fast. How can I overcome the pain?

On their side, there has been a process of emotionally and mentally checking out while you were still together and while you were under the impression that everything is cool.

What they do doesn't matter and it's completely irrelevant to your healing process, though it’s valid to hate and judge them harshly for leaving the way they did.

So, don't try to compete with them.

What are some effective strategies for getting more upvotes on Quora?

This is why you can't expect them to feel anything close to what you're feeling right now, because you and them are on a completely different stage in the healing process.

I.e. you thought that you had the perfect deal whereas they had already made up their mind and just weren't as emotionally invested in it as you were.

Instead, focus on taking care of, solving and healing what you are experiencing right now.

What should I do if I love a girl and she apparently doesn't love me?

This happened long or shortly before they physically left.

And during this process, they either started seeing someone new who they planned to secure as their rebound option or were busy creating their post-breakup plan.

This is why comparing yourself to them in terms of the healing process isn't going to help you in any way, shape or form.

Why can't NASA just bite the bullet and launch a plainly simple mission, audited by flat earther peers start to finish that definitively proves to even the smallest minds that the earth is an oblong spheroid, and not flat?

You both are on polar opposites of the scale.

Simply put, because they have been prepared and you weren't.