Neither bulls nor bears should be too confident as to what's next, argues Oaktree Capital's Howard Marks in his latest memo, aptly titled Uncertainty. History isn't relevant to today; if you've never experienced something before, says Marks, you can't say you know how it will turn out.

The note lists 25 important questions regarding Covid-19 that remain unanswered, before asking investors to think of the many unanswered questions that pertain to other factors such as the economy, oil prices and the US Federal Reserve.

"Who can respond to this many questions, come up with valid answers, consider their interaction, appropriately weight the various considerations on the basis of their importance, and process them for a useful conclusion regarding the virus's impact?" Marks's note brings to mind the words of the late John Templeton: an investor who has all the answers doesn't even understand the questions.