A person is not to be treated as unable to make a decision merely because they make an unwise decision.
Arguably one of the most important factors of the MCA, the right to make an unwise decision was set into legislation to take into account the very individual culture, beliefs, values and characteristics each person has which can influence their decision making.
We all have the ability to make a decision, with capacity, which another person may believe to be unwise; from the everyday buying of a lottery ticket or consuming alcohol, to refusing medical treatment based on religious beliefs. The individual must not be regarded as lacking capacity simply because another believes their decision is unwise. However, where an individual repeatedly makes unwise decisions which leaves them at significant risk, or their unwise decision appears irrational or out of character, this may be of concern and warrant further exploration with the individual. Professionals needs to consider not just whether or not the patient has capacity, but also whether there are other factors, such as whether the person is under pressure from someone else to make this decision.
A case study example is available to support this information - Unwise Decisions.