|Sally Simpson: 23.dxe4 does seem the better move.
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So what was going through his mind.
Is it controlling several important diagonals. It cannot move.
What you want is that Knight on that d5 square and with the Bishop glued on d5 that is not going to happen.
What is to happen with the Knight if it cannnot go to d5.
Also taking back with the Bishop on e4 encourages Black to trade his annoying Knight on c5.
Taking back with the Bishop on e4 gives White a clear target on e6. If he could move that Bishop from d5 he could work on e6 - but where?
And round and round your thoughts go.
It's dead easy to talk yourself into making possibly the wrong decision.
Throw into the pot that Nimzovitch had a very bad tournament finishing 11th from a field of 14, winning 1, losing 5 and drawing 7.
Add in Ray Keene's comment from his game from the same tournament with Mieses.
"when Nimzo got it wrong he really got it wrong!"
Nimzowitsch vs Mieses, 1920
And there you have it.
He was way off form and a few years away from being the brilliant player he became.