Think of a proverb or a well-known saying that relates to your writing topic and that cannot be attributed to a certain individual but is recognizable in your particular society. Integrate this saying into your piece of writing. For example, you could write, "It is said that 'the early bird catches the worm,' and this is certainly true in the lives of college students." Here, you do not need to define your source, as the saying is an anonymous and widely known one that you have placed in quotes and are not trying to take credit for yourself.
Think of an idea that is central to your specific discipline and is well known to all those in the field. In literature studies, for example, most people are familiar with the poetic theories of Pound and Eliot, so if you were to reference the "objective correlative," and your audience was a literary one, you would not necessarily need to further define this reference, as your readers would know what it signifies and where it comes from.
Put this idea into a sentence that relates to your topic. For example, you might write, "if 'hope is a thing with feathers,' in Dickinson's world, then it is here, in this poem, something quite different." Here, you do not need to define where the quote comes from or what it signifies, because your readers will recognize the famous line and understand it immediately.
Think of a general trend or mindset that you have observed in your culture and that relates directly to your writing topic. For example, if you are writing about depression, you might say, "People claim that their lives lack meaning and that they are sad all the time. What they don't know, however, is that fulfillment and happiness are within their power." Here, you are referencing a general trend rather than quoting an individual person or statement, therefore you do not need to further define your reference.