> How can one possibly say that A causes B, when B could very have caused A in a time-reversed view point?

There is an old joke about a mathematician and an engineer invited to kiss someone they both fancied if they got there first. The catch was they could only move half the distance towards the inviter each period.

While the mathematician fretted about Zeno's paradox preventing from convergence, the engineer got close enough to the inviter, eventually, to take them up on the offer.

LeCun is the mathematician in this analogy.

Note: he responded to Mukherjee's comment here. Why?

Mukherjee made a comment.

LeCun then responded.

The causal reason that LeCun responded is because Mukherjee commented.

There may be a host of associated factors -- perhaps LeCun only monitors comments while bouncing on a pogo stick in a large conference room and simultaneously sipping a latte. It doesn't matter. Because if LeCun were bouncing on a pogo stick in a conference room and sipping his latte, he would not have made the response if Mukherjee had not first commented.

So, we have clear existence of causality. If needs be, we could build an entire framework with that observational evidence.