Let’s start with intuition. What we usually refer to as intuition is our ability to understand something immediately without the need for conscious reasoning. We do this by taking all of our past knowledge on a subject, and then quickly coming up with a generalized idea. Humans tend to be really good at this and depending on the situation, it can be really good or really bad. Good because we can access information quickly; Bad because we overgeneralize.
What this means is that we make powerful associations with certain imagery almost instantaneously. And because these associations keep building on each other, what we end up with is a vast visual lexicon of symbols and shorthands that are utilized for communication every day. Long ago, stained glass illustrations decorated cathedrals to communicate to the illiterate masses. Though most people today in our society are literate, the same principles of communication are still being used today.
The next thing to note is that some symbols/imagery carry more historical weight than others. To illustrate, let’s look at a widely used icon that doesn’t carry much weight: