The de facto key-combination for copy-pasting, the programmer's butter-knife, for most people is Ctrl-C (for Copy), Ctrl-V (for Paste). In fact, it is possible that you are conditioned to hear Ctrl-C, Ctrl-V as "Copy, Paste". This is the combination advertised on most Edit menus nowadays (along with Ctrl-X for Cut).
However, coming from a DOS/Unix shell background, I used to find it difficult to press Ctrl-C for Copy because it had negative connotations for me. It used to be (and still is) the keys to press to cancel a running command in a console.
FYI, the same things can be done using
Ctrl-Insert = Copy
Shift-Insert = Paste
Shift-Delete = Cut
I thought this made good sense.
Copy? okay, it's a control insert with no display-change.
Cut? shift into the buffer after deleting it from the display
Paste? Shift out the thing in the buffer and insert it here
Ergonomically, this is in fact better if you do a lot of selecting with the shift-cursor key combinations. You could do everything with your right hand.
So why should it have changed? In this age of GUIs, most people do their selecting with the mouse (with their right hand) and could do the copying/cutting and pasting with their left hand! Personally, I am against selecting stuff with the mouse coz it's more strenuous.
Why Ctrl-C,X,V then? Physical proximity is the only rationale, no logic as in the former case. C for Copy, so get the others nearby.
Or was it because "X" looks like a scissors and you use it to cut! So get the others nearby?