What are the most important factors that negatively affect decision-making?

There are several important factors that influence decision making. Significant factors include past experiences, a variety of cognitive biases, an escalation of commitment and sunk outcomes, individual differences, including age and socioeconomic status, and a belief in personal relevance. These things all impact the decision making process and the decisions made.

Well, I think our mental bias is the most important barrier to us to make the right decision. There are also some other impacting factors... our environment, people around us, false news, wrong analysis, macro economic uncertainties, etc...