And why would it be viewed as a failure?
Because he/they will see 400 as being "low" and a "trend" much like he's inferring with TLJ being short of TFA. He will post dumb *** expectations and the film being short of those, random hack pieces from random websites claiming Kennedy/Star Wars is in danger, etc etc.
We'll likely hear comparisons to TPM and AotC, similar to those that were claiming Rogue One was a bust because of 40% reshoots.
Rogue made them all look stupid, I believe Solo can do the same. But even I realize it won't do the money Rogue did, but I feel 400/1bill is a fair expectation.