It is possible to look back and find many examples of trades that worked. To be fair we should add context.
Yes, John Smoltz became an elite player. You could have mentioned a few other details at the time of the trade. He was chosen in the 22nd round the previous season so he was not seen as a good prospect at that time. He was in the midst of his second season and was 4-10 with a 5.68 ERA. He had 86 strike outs and 81 walks in 130 innings.
So if the Twins trade Span for a player drafted in the 22nd round last year while scuffling through year 2, will you trust their scouting department to have found a gem like the Braves did in 1987?

