I would suggest that anyone interested in this subject read "The failure of capitalist production", by Andrew Kliman. The author delves into the tendency for the rate of profit to fall in marxist terms, looking especially, but not exclusively, at the 2008 crisis.
I mention this because he uses an analogy that made me understand the tendency for the rate of profit to fall more accurately: like gravity, the rate of profit tends to fall, but that does not mean that all objects on Earth will eventually reach their lowest point with no means of going back up. It is merely a tendency, which capitalism is always fighting back against, and not a deterministic prediction about an absolute low in the rate of profits in the future.