@jobo
When I was playing (American) football in high school, we'd run plays during practice. One day we ran the play wrong against our defense. So our coach stopped us and had us immediately run it again. We ran it correctly the second time, but guess what? The defense immediately stopped it. Our coach threw his clipboard in the air and said "off course you'd stop it, you knew exactly what was coming at you!"
Failed miserably against a fully resisting partner in practice. Worked perfectly against our opponent that week who didn't know it was coming. Actually, the play worked against several teams when we ran it at the right time and the right way. Never worked when they were expecting it though. Same as every play we ran throughout my career.
Odd... something didn't work against a fully resisting partner/opponent when they knew it was coming, yet it worked very well when they weren't expecting it. Remind you of anything?