Never short a great company that sells at an expensive valuation. $Tesla(TSLA.US) is a great company with best-in-class technology, leverages key secular megatrends that generate true first movers’ advantage, has a significant manufacturing cost advantage, and is run by a visionary leader who is a magnet for engineering talent. But TSLA trades at an extended valuation (220x forward earnings vs +35% long-term earnings growth), which gives investors reason to not own it, but not a reason to short it.

There are plenty of bad companies that have weak products or competitive positions, can’t leverage key secular megatrends, have non-compelling brands, a high cost manufacturing structure, or management teams that can’t execute that I can short instead.