Why do we blunder?

Why do we blunder at chess? "Because we can" is one possible answer. "No idea" is probably just as good. But my favourite reason is the streakers defence. "It was a good idea at the time."
Here is a game from a Correspondence event I am currently directing. The reason I picked this game is that it is played between two reasonably strong players, and as a CC game, you would think the chances of an outright mistake are quite low. But on move 25 Black spots what looks like a good move, only to have it all go wrong two moves later. 27.Qd3 looked pretty obvious, so I'm not sure what Black was thinking. Maybe he saw a defence which had a flaw in it, or just decided that winning the exchange was good enough. It turns out it wasn't.

Jones,,Kenneth - Zhakarov,Oleg [C92]
Australian Candidate Masters, 2018

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O b5 6. Bb3 Be7 7. Re1 O-O 8. c3 d6 9. h3 Bb7 10. d4 Re8 11. Nbd2 Bf8 12. a4 h6 13. Bc2 exd4 14. cxd4 Nb4 15. Bb1 c5 16. d5 Nd7 17. Ra3 f5 18. Nh2 bxa4 19. Rxa4 Kh8 20. Ra3 fxe4 21. Nxe4 Nxd5 22. Ng4 Re6 23. Rd3 N7b6 24. Rg3 Qe8 25. Kh2 Nc3 26. Nxc3 Rxe1 27. Qd3 g6 28. Nxh6 Re6 29. Nf5 Nd7 30. Nh4 Ne5 31. Qd1 Qf7 32. f4 Be7 33. Nxg6+ Rxg6 34. Qh5+ Qh7 35. Qxh7+ Kxh7 36. fxe5 1-0