You can regret. You can rejoice. You can actually do both at the same time.
However, I don’t think you can honestly look at your life and say that every time something beneficial happened to you, something else was taken away.
We tell ourselves this stuff to make ourselves feel better when bad things happen, and then conveniently forget about how the system supposedly works when good things come along.
Seriously, if we lost something every time we gained something, why would any of us strive to achieve anything?
You can’t have everything you want, but missing out on something should make you reassess your priorities and refocus yourself on the next goal.
And yes, if you want something you usually have to put in some kind of investment, but that doesn’t mean you’ve lost anything. Nobody says they gained food by losing money.
You can either put some time and energy into being purposeful about what you try to achieve in life, or you can just let things happen and make up sayings to make yourself feel better about the outcome.
It’s not about your outlook. It’s about your actions.