If we can't see, smell, or touch it, if scientists at leading universities have not conclusively studied it, then it isn't real, or at least it isn't worth bothering much about. And so it tends to go with the angels. You ordinarily can't see them, smell them, touch them, or subject them to scientific studies. You usually don't notice the work of the angels, they are rather bashful, though I don't doubt that there are some who might have seen one, or at least suspected their presence. The angels don't want to be noticed, nor do they want to be the greatest.
People always seem to mistake the presence of angels for something else.
Some people to think they are seeing Jesus. According to the Revelation of St. John, the sight of Jesus in His glory would be enough to knock us dead. Besides, the next time Jesus makes a visible appearance, it will be for all the world to see on the Day to end all the days when He raises dead. Others tend to think they are seeing Mary or one of the saints, but they are with the Lord, where all the saints who trust in the Lord Jesus are, and their bodies sleep until the resurrection. In all likelihood, when people see or sense some sort of heavenly being, it is most likely an angel.