Humans brains can store enormous amounts of information. Even so, they can only think about a few things at a time. Try to think about more than around five things, and your brain can't get much work done.
Programs can have thousands of steps, way more than our brains can handle. What to do?
Break a task into a few subtasks. Pick one of the subtasks and start working on it. Ignore the other subtasks for now; that gives your brain less to think about. Break the subtask into a few subsubtasks. Pick one to work on. And so on.