If you are a minority shareholder in a private company, you are unlikely to lose value in one dramatic event. It usually happens gradually: a capital increase priced too low, a contract with a company owned by the majority shareholder, management fees that grow faster than the business, or a dividend policy that suits one shareholder but not the others.
Each of these may have a good business reason. The problem is that they often go through without anyone checking them on your behalf, because you have no board seat, no direct contact with management and no routine of asking questions.
What you can do
A strong shareholder agreement helps, but your rights only matter if someone uses them. The best protection is regular, informed attention: reading the accounts and board papers, asking for the information you are entitled to, and raising questions early, while decisions can still be changed.
If you can get a board or committee seat, give it to someone with the time and experience to use it well. If you cannot, regular and professional contact with the majority shareholder often achieves more than a formal dispute.
A minority investment requires ongoing engagement with fellow shareholders, active monitoring, and a clear understanding of governance and exit rights.