Diversity in industries, uniformity in time horizons

I think the only way to beat the market is to diversify. The market is too difficult and unpredictable to be able to time and understand correctly. Certain markets are correlated, so investing in uncorrelated markets is also another way to make sure to diversify risk.

Some people filter markets by industries, but I prefer to filter by estimated time horizons first. For example, I like long term plays - so I like buying and holding anything that I think has long term potential. I care about industries only in the sense that I think it’s either long term or not.

For me, long term investing represents the philosophy that I really don’t know the market. Anything sufficiently long term is impossible to know, no matter who says they have the crystal ball. On the other hand, if I think short term then that would assume I know the market and can time it, which runs counter to my assumptions.