At this exact moment, things cannot be different than they are.
Can you see this simpler than simple, invisibly obvious fact?
Everything that has ever happened, since before time was time, has led up to this moment being just as it is.
Therefore, this exact moment could not, would not, and should not be different. It can’t be.
In your experience, have you ever been able to change a moment once it arrives?
In your experience, could anything have been done differently than it was? Even if you appeared to have choices, could you go back in time and make a “better” one? Is that possible?
So, could you have done something differently? No, because you didn’t. Provably.
In your experience, would you have done something differently? Would can only occur as thought-based hindsight; it has nothing to do with reality in real time. Would is the imagination playing an after-the-fact game of countless assumptions.
So, would you have done something differently? No, because you didn’t. Provably.
In your experience, should you do something differently than you did? Should combines the past-dwelling component of could and the hindsight game of would into a finger-wagging, judgmental directive. “You should have known better!”
So, should you have known better? No, because you didn’t. Provably.
Check this for yourself:
Is there some parallel version of you that could, would, or should be any different than it is right now?
Outside the acrobatics of complex thought, do could, would, and should have any meaning or value whatsoever?
Can a could, would, or should thought EVER be believed as "true"? Who are those thoughts even referring to?
What if the “-Ouldiverse” (i.e., every could, would, or should that comes to mind) has only ever existed as passing thought that naturally comes and goes of its own accord?