The Houston Astros traded Kenny Lofton before he really got a chance at contributing because of a guy later on this list. He went on to have an incredible 5 year stretch where he hit .316 and stole 325 bases. He went on to have an illustrious career and the Astros could have really used him and the guys they got were below average player.
Curt Schilling, like another guy on this list, never played ball in the majors for the Astros but he was traded for a guy that never played ball in the majors for the Astros either. Instead, the Astros got to watch him be a dominant pitcher for over a decade in the league.
John Mayberry was a young guy that struggled with contact but whenever he made it, could launch the ball out of the stadium. This trade pairs with another further down the list that is just infuriating. The team needed a power bat at first base but traded away a youngster who could do just that.
The Houston Astros traded Hunter Pence in the middle of his prime. He had made a couple of All-Star teams and provided consist power and average for some pretty decent Astros teams. The return wound up not being super great which lands it in the honorable mention section. He had some really good years after he left.
Roy Oswalt was traded at the beginning of the end of his career as the Astros were finally giving into full rebuild mode. The return was worse for him but fans, fortunately, didn’t have to watch him have great success elsewhere. Michael Bourn was traded after some really good seasons and the return, again, wasn’t great.