Selling Bitcoin would always be a stupid decision, because the price could be always higher. But there are people who just don't want to invest anymore and they are retiring, for an example, people who bought Bitcoins for $1 each don't need to wait anymore, they are already rich and they can retire.
It is not a stupid thing since we do have different targets and aim in our life, let us just respect each others decisions with their investment, as they should learn by it if they thought they loss their investment by selling at early time, but don't hate them let us just inform them and teach them the right thing.