In order to cope with this limitation, we need to aggregate concepts, translating a large number of generic concepts into a smaller number of more specailized ones. Instead of holding concept A, B, and C in mind all at once, we need to create a new single concept ABC which combines the relevant parts of the other three.
This process is a special case of the general concept linkage process already discussed, but it's a sufficiently common and important special case that it merits its own discussion. Thus, let us consider this case in which several fairly generic building blocks combine to link to a much more specific overall concept, like certain combinations of letters turn into words. We'll call this special case "pattern matching." The purpose of a pattern match is to simplify information by sorting it into categories according to the relevant properties, and ignoring the irrelevant or useless properties. This condenses several concepts into one, freeing up the slots to be used for further thought.
For a fairly straightforward example, consider reading. When you look at a page of text, your unconscious sorts the lines and dots into letters for you, and presents to you these letters. You can look at letters written in different fonts, scripts, or handwritings, and recognize that they are all the "same". Here, the relevant property is the symbol that the mark is intended to convey; the style of the mark is an irrelevant property.
Usually the pattern match will depend on the sensory stimulus plus one or two concepts already in mind indicating the properties or type of information you're interested in. Which properties are relevant depends on the situation. If your goal were to set type to match a particular sample, you might look at the sample and come away thinking about the typeface which was used, without having paid any attention to what was actually written. Here, the relevant property was the style of the marks, and the actual symbols conveyed by the marks were irrelevant.
Once a pattern match has been performed, its result is available as fodder for use in another level of pattern matches. Once we've identified some marks as letters, for example, the stage is set for then identifying these letters as words. Both of these steps can happen automatically, such that when you read in normal circumstances, you have no or only a very dim conscious awareness of the letters; you go straight from the visual perception to the words.
Pattern matching - the process of simplifying several concepts into one - is extremely common and important, and is well worth noting as a mental process.