There are several ways to inhibit processing through barriers and bias; these represent the four most common barriers to effective problem solving.
Essentially, functional fixedness is the inability to see beyond the box. For many people, they see a match box, and only believe it is used for matches. However, if the box is emptied, it can take on another use. In problem solving, functional fixedness does not allow creativity to take hold. Problem solvers do not refer to their topic as having endless options, because they become hung up on traditional solutions.
This is the knew-it-all-along, or predictability bias. In this case, problem solvers believe they know the outcome with greater certainty than they should have. This bias leads people to overlook key elements, forget to weigh options, and potentially rush hastily into decisions or outcomes.
Of all of the barriers to effective problem solving, this may be the most dangerous one. In the case of confirmation bias, problem solvers do not accept information that contradicts their preconceived ideas. Instead, problem solvers only account for the information that lines up with their widely held beliefs. Clearly, this kind of bias inhibits true cost to benefit analysis, research is skewed, and problems are ineffectively, if at all, solved.
People have a general tendency to relate back, and fall back to what they have always done. These are called heuristics. In problem solving, though, this is considered a mental set. For the problem solver, mental sets keep people from solving problems in new and creative ways. Instead, they rely on, and revert back to how they have always done something, even if that option doesn't work or isn't as effective.