I sealed a salmon fillet in a ziplock bag using the water displacement method I saw in a video. Looked sealed to me. Twenty minutes into cooking, the bag was floating and half full of water.
The fish came out waterlogged and tasteless. I had people coming over in an hour and no backup plan.
Where I Went Wrong
I did not seal the bag properly before submerging it. Air pockets remained, and water pressure found every gap. The displacement method works, but only if you work slowly and seal at the last possible second.
I also learned that not all bags are equal. Thin sandwich bags fail under sustained heat and water pressure. You need actual freezer bags at minimum.
What Changed
I bought a cheap vacuum sealer for thirty dollars. It paid for itself the first time I did not have to redo dinner. For ziplock bags, I now do a test run with just water to check the seal before adding food.
The method is only as reliable as your seal. That lesson cost me one ruined dinner and a lot of unnecessary stress.