Take for instance the real estate market that everyone thought was a sound and safe market to invest their funds into... and what happened? World wide investors lost their shirt and leaped to their death.
The key for investing in films is looking at the filmmakers proposal. Look at the introduction sheet A.K.A. Executive Summary, which is basically extracted from the Business Plan. Once the executive summary convinces you to go to the next level, review the business plan.
Check the Organization Chart and see how the production company is setup. Determine where you are within that organization. Have they fit you in as an important element they take in consideration when using your capital? Or do the filmmaker just wants your money and hope for the best?
Investing in a film is making a specific, calculated, and safe investment as any other investment in the market