I really like this list of What They Used to Teach You at Stanford Business School, written by a guy who was class of 1972 and spent most of his career in i-banking. It addresses many of my beliefs about investing and investment research, particularly the overreliance on formulas and extrapolation of observed data. You can read the full article (from Portfolio.com) here.
- Don't use many financial ratios or formulas, and when you've picked the few that will actually tell you what you want to know, don't believe them very much (Prof. James T.S. Porterfield);
- Remember that any damn fool can compute an IRR or DCF. The trick is to find a business that can return 20% after tax, understand its critical indigenous and exogenous variables, and then run it so it meets its return target. (Prof. Alexander Robichek.)
- Always ask what can go wrong (Porterfield);
- Never extrapolate beyond the observed points of a distribution, you have absolutely no information outside the observed range (Prof. J. Michael Harrison);
- Remember that you can always break the bank at Monte Carlo by doubling your bet on red at the roulette table every time you lose. The problem is it will break you first; It's called "the takeout." Therefore, always manage your financial structure so that takeout is not an issue. (Porterfield.)
- Big M (today Nassim Taleb's Black Swan) is never a part of the optimal solution. If it shows up in the answer with any coefficient greater than zero, you have the wrong answer and have to continue to do program iterations. (Harrison.)
- There is never any excuse for looking through the substance of an economic transaction, whatever the accounting, and if the accounting permits you to do so, it's wrong (Prof. Charles T. Horngren.)