If you trade for a guy with clean mechanics who can throw 97 MPH and has had good numbers in his career, then three weeks later he blows his shoulder out and he comes back and never tops 91 and can't get it done, does it mean you made a bad trade? Not in my mind. If we had a time machine would you take it back? Of course, but that doesn't mean it was a bad idea to make the trade, it just means it didn't work out.
If I am playing blackjack and the dealer is showing a 5 and I am sitting on 10, I am going to double down on that. It was the right move. If the dealer flips over a 6 and then gets a 10 it doesn't mean I made a bad bet, it means it didn't work out. There is a big difference between a bad trade and a trade that didn't work out.
I will judge a trade by how things looked at the time they were made and the information that was available at the time.