A very pivotal issue in philosophy, and in establishing the credibility of science, was the problem of induction pointed out by Hume. The problem of induction, also known as the Is-Ought fallacy, was that scientific knowledge can’t be considered truthful or actually valid as it assumed that the past reflected how the future is going to be; that from observations of past events we can somehow make proofs of future events. This assumption is one that is not logical, and instead just an aspect of human psychology we use to keep us from essentially going crazy.
Popper side-steps this “skeleton in the cabinet” of philosophy by establishing how science has nothing to do with induction. The key distinction he makes is that we’re not using the past as proof of how the universe works, and instead use observation to form a theory and then using the future to falsify it. This makes knowledge and science a never-ending attempt at moving toward truth and knowledge rather than making universal Is-Ought assumptions. So what we are then trying to achieve are a “best current answer” with the awareness of our potential ignorance, and instead compare our current knowledge and ability to explain compared to the problems of our past theories; the goal then becomes to falsify our current knowledge to create new ideas rather than trying to rigidly rely on assumptions from the past.