Identifying principles and thought processes to use in locating a +3.2 or similar move [Title &quot;indrekaavik-Swifty15, chess.com, 5/3/2021&quot;]
[FEN &quot;&quot;]
[startply &quot;29&quot;]

1. e4 c6 2. d4 d5 3. e5 Bf5 4. Nf3 e6 5. h3 c5 6. c4 Nc6 7. cxd5 exd5 8. Bb5 Qa5+ 9. Nc3 cxd4 10. Nxd4 Bd7 11. O-O Nxd4 12. Qxd4 Bxb5 13. Qxd5 a6 14. Rd1 Rd8 Qf3 Ne7 16. Bd2 Ng6 17. Qxb7 Nxe5 18. Nxb5 Rxd2 19. Qb8+ Qd8 20. Qxe5+ Be7 Rxd2 Qxd2 22. Nc7+ Kf8 23. Nd5 Qg5 24. Qb8+ Bd8 25. Rd1 g6 26. g3 Kg7 27. h4 Qh5 28. Nf4 Qxd1+ 29. Kh2 Bxh4 30. Qe5+ Bf6 31. Qe4 Qf1 32. Nh3 h5 33. Qb7 h4 Qb3 hxg3+ 35. Qxg3 Qe1 36. Kg2 Qe4+ 37. Kf1 Bxb2 38. Nf4 Qb1+ 39. Ke2 Rh1 Nd3 Qd1+ 41. Ke3 Re1+ 42. Nxe1 Qxe1+ 43. Kf4 Qb4+ 44. Kf3 Qc3+ 45. Kg2 Qxg3+ Kxg3 Bd4 47. Kf3 f5 48. a3 g5 49. a4 g4+ 50. Kf4 Be5+ 51. Kxf5 g3 52. fxg3 

I'd like to improve my thought process when considering a move, but I don't understand what rules/principles to apply to a particular situation where I got it wrong. This happened in the above game I played as black on chess.com. I am aware that I made plenty of mistakes before and after the move, but those I understand. I am rated 1200.
I discounted the rook exchange 15... Rxd1. After the game, the engine told me I would have had a +3.2 advantage if I had made the exchange. I can't work out why it creates that advantage.
I considered the exchange, but I thought I would stay disciplined and principled. I remembered GM Smirnov's rule &quot;to take is a mistake. I have been reading in IM Silman's '&quot;The Amateur Mind.&quot; It teaches that a simple one-move capture, attack, or check is pointless if it can be easily parried.
My thinking was that exchanging rooks MIGHT be useful if I gained a tempo by sending my opponent's knight to the back rank. But I saw when that they could just recapture with their queen and take control of the d file. It didn't seem that I had anything to gain. As such, I just continued to develop my pieces.
Can anyone explain why this was such a critical move, and the thought processes I could have used to identify it?
This position is more complicated than it first looks!  You need to see more than one move deep to understand the difference between 15...Rxd1 and other moves.
As Scounged has pointed out, you already have an advantage of about +3 because you're a piece up.  The problem is that white is attacking your pawn on b7.  So some time soon, you want to play a move like ...Bc6 to defend that pawn.  In fact, if you play ...Bc6 right away, it's almost as good as ...Rxd1.  But the computer thinks it's even better to play 15...Rxd1+ 16. Qxd1 Bc6.
With your chosen move, white missed an opportunity.
Option 1: 15...Ne7 16.  Qxb7 doesn't work for white, because of 16...Rxd1+ 17. Nxd1 Qe1+ winning the knight.
Option 2: 15...Ne7 16. Rxd8+ Qxd8 17. Qxb7, and now white has two pawns in exchange for the bishop, and the game is almost on equal terms (black is still ahead, but it's not as good as if you'd played 15...Rxd1).
Suggestion: if you don't already know the word &quot;zwischenzug&quot;, look it up and think about how it relates to this position. Sometimes the engine isn't really telling you about the next move, but pointing out something further along the sequence.