Organizing my LEGO collection has given me a good chance to reflect how our memory and vision (among other things) work. Trying to find a certain piece among the lot is a good exercise to observe these functions. By better understand them helps to improve the overall efficiency of the process.
The most effective way finding certain pieces would be to just keep everything in one pile and go through it every time. The problem is we can only keep a certain small number of things in our mind, in our working memory. I can keep about 10-12 things in my mind. That's not nearly enough as usually there are hundreds of pieces that need to be found. And keeping all those pieces in mind isn't enough.
Another limitation is our vision, or actually perception. I can see all those pieces in front of me, but if I'm not actively looking for something it's all just meaningless information our minds just filters out. To find anything I need to be looking for certain things. And that requires even more "processing power" than just keeping things in mind. Usually I can look up maybe 3-4 things at the same time.