The irony of assumption
No one wants to feel the earth-shattering weight of their lack of knowledge, leading to Bacon's observation of this essential human irony. Although philosophers have long noted that not thought is not all perfectly reasonable (like Aristotle's own Organon, for instance), that hasn't really stopped humans from being assumptive about reality. Bacon says before a person can be scientific, they have to be willing to relinquish the assumptions they hold about reality.
The irony of testing
Bacon's portrait of science is essentially ironic, philosophically speaking, because he believes that by nature, humans believe ideas to be true that, when they actually start testing, they are instantly placed back in the role of a curious observer, learning from reality. That means that science is literally predicated on dramatic irony, because it assumes that humans are probably misunderstanding reality, thus needing to test in the first place.
Bias confirmation
Bacon notices that there is an additional layer of irony in the equation of reality: Human assumption is doubly dangerous because people tend to find the kind of data that supports their ideas, even if they're wrong, so ironically, without science, people tend to resort to bias confirmation almost exclusively, by the design of the human mind or by nature, or both. Bacon urges the reader to consider true observation and the humility of understanding that one might be mistaken about literally every one of their beliefs.
Secularization and religious science
Although Bacon's view of science is mechanistic and non-religious, his opinions about science are undeniably rooted in his philosophical religion, because he interprets his Christian faith in a way that makes him feel science is literally his religious duty. He says that by understanding "Truth" appropriately, humans have a chance to improve their decrepit fallen state back toward the original bliss and wonder that humans were designed to enjoy. He sees science as the true answer to the brokenness of the earth. Oddly, this conviction leads him to abandon religious assumptions about reality in the hopes of finding the real Truth.
The irony of human animal nature
Of course, this scientific treatise is predicated on this important irony. Why do humans improperly understand their reality? Why do they take so much for granted in their beliefs? Bacon's answer for this is that it is because humans are animals with biological needs that shape our perspectives of reality. This is very important to notice, because it helps Bacon to construct a kind of 'tabula rasa' to do science from. He hopes the experimenter will be able to override his tendency to overlook details that don't seem important in his mind, but might be significant in ways the experimenter hasn't considered. It goes against human nature to think this way, says Bacon.
