Principle three of the Mental Capacity Act says that
"a person is not to be treated as unable to make a decision merely because they make an unwise decision"
Haven't you ever made a silly decision before that you later wish you hadn't! And the reason you were not challenged on this, despite the good advice and words of wisdom you received, was because you had capacity to do so.
We are all so very different. We have our own values, beliefs, preferences and attitudes and with this comes different perspectives about what is sensible and what is not. No-one has the right to judge a decision you make no matter how unwise.
However, when a person has capacity issues an unwise decision may be an indicator of a bigger problem. To make a decision you need to fully understand what it is you are being asked. This requires not just an understanding of the question but also an understanding of the risks and benefits and the consequences of doing or not doing something. There may be a reason to question capacity if someone repeatedly makes unwise decisions that put them at significant risk of harm or exploitation or makes a decision which is obviously irrational or completely out of character. But this is not enough in itself to decide that someone lacks capacity. There needs to be further investigation into the individuals' past decisions, choices and expressions of wish and intent; could there be a medical condition such as paranoia that is causing impaired judgment, are they subject to undue influence or do they have all the information required to make the decision.
So, from now on, let's not judge silly decisions as being unwise but take the time to look at the surrounding circumstances and the individual to see what is really going on as it may be a symptom of a bigger issue.