Of course it is. Psychology is incredibly powerful.
Psychology is probably the wrong word, it at least needs qualification. I'm thinking more of mentality and expectations based on largely irrelevant traditions. In the context of whether or not psychology should be an excuse for professional athletes it is more than a pedantic and poorly expressed distinction.
Teams don't even try to chase 500+. They seize up because the history books say that it can't be done which doesn't really have account of the fact that pitches have been much more durable in the last 15 or so years. There is now the convenient modern dogma that "you have to take the good with the bad as far as
attacking impatient and lazy one day specialist batsman X is concerned". It has given chasing teams the perfect get out clause because not many modern players bother digging in and they're not scrutinized for it because "they never had a chance anyway".
The WACA pitch looks like a minefield but is playing as true as it was on Sunday and Monday when Australia was piling on runs. Cook is the only guy to be undone by the pitch so far.
Pietersen simply doesn't place a high enough price on his wicket. He hardly seemed to be crushed by the weight of expectation as he coasted to 45. Bell and Stokes had already given up and were just having a hit. I suppose Stokes, in particular, may never had played well if he was faced with the pressure of being able to win the match but it hasn't even gotten to that point yet.
I could stomach them seizing up at 3 for 250 to 300 tomorrow morning as the pressure built but collapsing to 5 for not many again, with 3 players getting themselves out, is not the forgivable result of psychology it is just laziness justified by an obsession with tradition.