You have to be able to develop long-term working relationships with people of high character. This extends beyond treating their clients with respect. They have to also be good to their employees. The arrogant, self-absorbed portfolio manager might be a great investor, but odds are eventually they’ll come back to haunt you at some point. And if a fund manager makes it sound like they’re doing you a favor by letting you invest in their fund, it’s probably best to sit that one out.
BTW, my very worst investment was about twenty years ago, when I started to have money to invest. I discovered a recently created "closed" fund by Bank HaPoalim, that proposed to exploit the contacts of the bank and identify the best technological startups. The Bank put up half of the seed capital of the fund. The manager was an experienced banker. It looked good. I went to Oody, my "friend" in the bank, and asked for details. Oody showed surprise "How do you know about the fund?" and hesitantly, said he will try to obtain a share for me. It was very expensive, 40,000 shekel share, and I bought two. When I saw the detailed investments of the fund I was much disappointed: it included a toy computer to teach computing to babies of 2 -3 years. I had examined that startup at Tel Aviv University and concluded it was absurd. Effectively, it folded not long after. Another thing I learned is that the fund managers took 2 million dollars per year for office expenses. Obviously, they were out to steal my money. But I persisted even when the fund was liquidated. They offered to pay me off with a few thousand dollars or keep my shares. I suspected they wanted to buy back my shares for noting and rejected the offer. I lost all my money. I opened an account in another bank.