There is a distinguishing feature of life: life fights for its continued existence. People are now a leading lifeform on Earth because of the powers of thought, including the ability for advanced abstraction. This talent varies, but many elements of thought are common.
Not many people think about how they think. Fortunately, the scientific method both exposes the weaknesses common in individual thought and allows those weaknesses to be addressed. You can improve your capabilities by recognizing how you form beliefs.
Ideas are acquired by observation. The individual can seek out data, or it can be imposed. It is in the acquisition and use of this data that individuals fail, and frequently.
Early in the investigative sciences, it was recognized that a single type of test, repeated, could return inconsistent results, as a result of ineffective controls on variables possible in testing. Surprisingly, a number of people could be fooled by the same test if they didn't recognize the lack of controls. This led to two things: a requirement of reputable scientists to publish the means of their determinations for peer review, and a way to determine fallacies of observation.
You can see a fine example of fallacies - some of which you've never suspected - at The Nizkor Project, and obtain a tutorial, which will help you eliminate flaws in your own reasoning, at the Fallacy Tutorial site.
When careful measurements were made possible, it was discovered that no two measurements were ever exactly alike. This made the science of statistics necessary and extremely important, as it was revealed that certainty only exists by definition.
Now, statistics is probably (pun intended) not what you think it is. Although lots of people think of statistics as a way for politicians to lie to them, the precision of manufacturing processes has made the science an essential part of everyday life.
As an individual, you are essentially an underfunded research company. You have to constantly make decisions as to what information is important, and then you have to figure out which information you have is correct.
But what does "correct" mean?
Unconsciously, you define "success" every time you are satisfied with something you do. Clearly, it doesn't bother you that pi has no end, when you can select a few decimal points and get the level of precision you need.
When you research an idea, you are limited by time and ability as to the amount of consideration you can devote to the task. Family and other distractions take time; sometimes, investigation requires special tools unavailable to you; the mental acuity and agility you can bring to bear may be insufficient to the task. At some point, the perceived return on investment - effort expended vs. gain achieved - reaches a zero, and investigation stops. At this point, the belief is "filed" as a mental "base" upon which future decisions can be made.
Our perceptions have two major limitations: prejudice, which includes everything a person thinks he or she knows, and acumen, the physical means with which we can investigate something brought to our attention.
Because of physical limitations and the innate process of judgment, your investigation cannot be complete. This means that whatever the belief, it cannot be the "whole story". It can only be good enough for you to continue on to other issues.
This does not change, is not affected, by your own prowess in your chosen field. Be proud of your achievements, but don't think that automatically conveys expertise or authority to you in another. If you did that, you would be wrong.