Its frustrating, but it happens.
I brought back a former FA after the start of the season in Clemente this year. Long reliever. He was asking for about $12 mil over 3 years after the previous season. So I let him go, and no one signed him, so after the new season began, I was able to bring him back for only about $1.2 million to beef up my bullpen.
Sure enough, got 3 appearances (2.1 innings) out of him before he went down for 159 days, during a cycle in which he didn't even pitch. Having no one at AAA that I trusted to replace him, I then had to go sign another LH long relief guy a couple days after signing the first one. While not the only reason, the extra money spent is a major contributor to me not having the funds to sign one of my higher draft picks right now.