I've been an angel investor for quite a few years, and I've made lots of mistakes along the way. In the beginning I would invest through networks and syndicates and this had lots of advantages because it accelerated my learning process. I could piggyback on the wisdom of others who had been doing it for many more years.
This had its own set of issues however. For example, the process can be fairly bureaucratic because it takes time to get everyone on the same page, and this can be frustrating. Because there are so many people involved, there would often be differences of opinions - for example, when it was time to raise the next round, some of us would be supportive, while others would not.