Trades that have backfired/set your team back

Would be curious to hear owners discuss win now trades that have set your team back or severely backfired? I am usually A proponent of trading picks/ overpaying for someone you think will get your team over the top when you are contending.

What are some big moves that you have made in the past that still haunt your team today?

Edit: loving the feedback in this thread! Common theme: We all have made terrible decisions.