The reason we misplace items, which we blame our memory for, is simple. We were not consciously thinking about it when we put it down, because we were operating on auto-pilot-mode. We were not focusing on what we were doing – in effect, “we” were never “there”, which is why we can not consciously recall where we put the wallet.
The subconscious mind will know where it is.
However, since we engage with the world through our conscious mind, the wallet is as good as lost. This will inevitably happen more often as we grow older, not because our memory is getting worse, but because we have more memories and associations. As a result, our conscious mind is going to be distracted more often, making it harder to concentrate on what we are doing, especially on easy everyday activities.