Regret? Why should i?
There's nothing to regret. Everything happens for a reason.

In physics every particle in motion follows a single principle.
That principle states that a trajectory of a motion only happens in the minimum action possible.
That explains why apple falls in a straight lines, while lightning bolt moves in a zig-zag. Some might said it was meant to be. I said, it's the least action principle.

We are particles in motions. Our conscience appears because of that principle.
Brain communicates using an electric charge carried by a particle called electron. And guess what? Electrons are particles.

We are just bunch of moving particles. Following a principle called the least action principle.
We are particles in motions. We always move with the minimum action possible.
Whether we liked it
or not.

So, indeed it is. Everything is indeed happen for a reason. To spend the minimum action.
That's why we're in love. Because at that moment that's the least action possible.
That's why we're left alone. Because that's the least action possible.
That's why we fall. Because that's the least action possible.
That's why we're trying to get back up. Because that's the least action possible.
That's why we gave up. Because that's the least action possible.
That's why,
we are the way we are.

So why should we regret? We spend the least action possible.
Unless, the least action possible is by regretting.
Unless, the least action possible is to stop moving.