user20569: I received the following tactics puzzle on lichess.org. Even though, I ended up solving it correctly, I am still not clear about the move 2. Ng5, because this loses the Queen. What prevents 2. Qe2, which would save the White Queen.
[Title "lichess puzzle 61506"]
[FEN "rn2k3/1b1p1p1N/4pBrb/qp2P3/3P3P/pP1Q4/P4PP1/R2K1B1R b q - 2 19"]

1... Be4 2. Ng5 Bxd3 (2. Qe2 *)


user19877: The other "motivation" is that it is simply the best move per the computer, that is if a computer can have a "motivation", per se. 
That is a problem with tactics problems on Lichess, Chess.com, and ChessBase.com...they often do not take into consideration the best human response, which may be harder for the human to see to the end, but the eval is not as good to the computer.
That happens a lot in their tactics problems. 

user4418: 
What prevents 2. Qe2, which would save the White Queen?

White's problem is the mating threats from the bishop battery and queen after Qc3. For instance:
[Title "lichess puzzle 61506"]
[FEN "rn2k3/1b1p1p1N/4pBrb/qp2P3/3P3P/pP1Q4/P4PP1/R2K1B1R b q - 2 19"]

1... Be4 2. Qe2 Qc3 3. Rb1 Qxd4+ 4. Ke1 Qc3+ 5. Kd1 Bxb1 6. Bg5 Rxg5 7. hxg5 Bxh7

and White is lots of material down and still facing mate threats (Qa1)

20569: <p>I received the <a href="https://lichess.org/training/61506" rel="nofollow noreferrer">following tactics puzzle</a> on lichess.org. Even though, I ended up solving it correctly, I am still not clear about the move <code>2. Ng5</code>, because this loses the Queen. What prevents <code>2. Qe2</code>, which would save the White Queen.</p>

<pre><code>[Title "lichess puzzle 61506"]
[FEN "rn2k3/1b1p1p1N/4pBrb/qp2P3/3P3P/pP1Q4/P4PP1/R2K1B1R b q - 2 19"]

1... Be4 2. Ng5 Bxd3 (2. Qe2 *)
</code></pre>
 19877: <p>The other "motivation" is that it is simply the best move per the computer, that is if a computer can have a "motivation", per se. </p>

<p>That is a problem with tactics problems on Lichess, Chess.com, and ChessBase.com...they often do not take into consideration the best human response, which may be harder for the human to see to the end, but the eval is not as good to the computer.</p>

<p>That happens a lot in their tactics problems. </p>
 4418: <blockquote>
  <p>What prevents 2. Qe2, which would save the White Queen?</p>
</blockquote>

<p>White's problem is the mating threats from the bishop battery and queen after Qc3. For instance:</p>

<pre><code>[Title "lichess puzzle 61506"]
[FEN "rn2k3/1b1p1p1N/4pBrb/qp2P3/3P3P/pP1Q4/P4PP1/R2K1B1R b q - 2 19"]

1... Be4 2. Qe2 Qc3 3. Rb1 Qxd4+ 4. Ke1 Qc3+ 5. Kd1 Bxb1 6. Bg5 Rxg5 7. hxg5 Bxh7
</code></pre>

<p>and White is lots of material down and still facing mate threats (Qa1)</p>
