Touch everything
Explanation based on my own experience:
I can’t find something. It’s literally right in front of me, but there is a mix of things and I JUST DON’T SEE IT. Grr.
I start on one side and start touch everything one at a time until it somehow magically appears. It was there the whole time.
If I sense that this type of thing is happening and I’m looking only visually, it’s not there. It’s just not there.
Touch works better than eyes.
For me I have to ask where it is. Literally. Ask out loud while I’m looking for it, typically to an audience of no one, but sometimes my gf, “Where in the FUCK is my ITEM?”. Without fail, my eyes will immediately land on the subject of the rhetorical query, and it is always on a surface that I have very nearly, but not quite, comprehensively searched multiple times.
I just replied to someone else saying that I do this. Sooo…yup. Good trick for those who haven’t tried it yet.