The only time that I've been careless I guess when I've pressed that convert or swap button of our local exchange when I have no freaking idea that I was selling the ones that I've held before. Yes, a complete noob and that's okay because I've learnt from it already.
That quick swap mistake I have done before, and it was not a nice one, especially when the rate was below the actual market rate as of that day since it was an automatic swap. it was not a funny one for me.
But sending to a wrong address, never happened to me. And it's due to the unique wallet addresses that we have. Unless a PC is infected by that malware copy pasta virus and you don't cross check addresses before sending then that's the only possibility that someone will fall for it.
If not for the fact that the clipboard virus became very popular and victims cried out, many of us would barely look at our wallet address when we are transacting, as long as it was copied, and even if we are to look, its always just the beginning and ending part of the wallet, but due to how the clipboard malware operates, its now important to gradually cross-check the wallet address from beginning to end, just to be sure it has not been replaced with a similar address.