To the level of your ability. I say this because I certainly but up against my limitation and at some point you have to recognize someone with expertise and take their advice. So you can decide things based on what you know but when you don't know things well enough you have to sorta meta decide. Medical is an obvious example. I will certainly do some internet research with my help and well being but when it comes to the yearly I have a discussion and listen to the advice of my doctor. I will decide if and how much of their advice to take but if im not taking their advice I should likely get another primary care as I obviously do not feel confident with their expertise. I may take into account what I think their biases are but I have to take into account what I think my own biases are as well. Im a pretty high functioning individual who has several degrees, pretty much liked school, and is used to learning new things regularly. There is no shame in recognizing and taking advice from someone who you think has better expertise than yourself. On the other hand some folks do just not even try and want any random person to just do their mental work. At the very least the person should look at what the decision is and evaluate their own capacities and have a reason why they want a particular someone to help them out.