user4399: Click here for engine re position below
8/3r4/1kp2p1p/ppRp2pP/3PP1P1/3K1P2/PP6/8 w - - 0 1

From hanging pawns in The Principle of Two Weaknesses in the Endgame at 9:02 (the game is discussed from 0:00 until 12:20).
The way Rd8 is described makes me think Rd8 is some natural defensive move in a rook endgame that is already winning for white.
But according to engine:

The position is actually about drawish after a3 (eval 0.2)
But the next move is critical: It seems that the only move that holds the draw is a4 (eval 0.1 or 0.2).
Meanwhile, the evaluation goes from 0.2 to 3.4 for (a3 and then) Rd8.

Thus, it seems like Rd8 cost black a drawn game rather than that Black didn't really have that much chance to draw(/win) from the start (of the endgame in the video).
What's going on?
Similar question: akiba rubinstein vs alexander alekhine 1911 rook endgame: the mistake here is Rxb5 right?

user11144: The mystery is easily solved if you just follow a few alternatives with the engine. The point is simply that if White comes to b4, the Rc5 gets another protection. This means that after exd5 Rxd5, White can march on with Ke4 as c5 is no longer hanging, and his activity wins in the long end (autoplay again). And cxd5 instead will immediately lead to zugzwang, and dxe4 is obviously (?) bad in any case. Thus not Rd8 is the cause of (probable) loss, but not blocking b4 in time.

4399: <p>Click <a href="https://lichess.org/analysis/standard/8/3r4/1kp2p1p/ppRp2pP/3PP1P1/3K1P2/PP6/8_w_-_-_0_1" rel="nofollow noreferrer">here for engine</a> re position below</p>
<pre><code>8/3r4/1kp2p1p/ppRp2pP/3PP1P1/3K1P2/PP6/8 w - - 0 1
</code></pre>
<p>From <a href="https://www.youtube.com/channel/UCkJdvwRC-oGPhRHW_XPNokg" rel="nofollow noreferrer">hanging pawns</a> in <a href="https://www.youtube.com/watch?v=KJ1jGqtIt2w&amp;lc=Ugwz9gva18rVg8R86nx4AaABAg" rel="nofollow noreferrer">The Principle of Two Weaknesses in the Endgame</a> at <a href="https://youtu.be/KJ1jGqtIt2w?t=542" rel="nofollow noreferrer">9:02</a> (the game is discussed from 0:00 until 12:20).</p>
<p>The way Rd8 is described makes me think Rd8 is some natural defensive move in a rook endgame that is already winning for white.</p>
<p>But according to <a href="https://lichess.org/analysis/standard/8/3r4/1kp2p1p/ppRp2pP/3PP1P1/3K1P2/PP6/8_w_-_-_0_1" rel="nofollow noreferrer">engine</a>:</p>
<ol>
<li>The position is actually about drawish after a3 (eval 0.2)</li>
<li>But the next move is critical: It seems that the only move that holds the draw is a4 (eval 0.1 or 0.2).</li>
<li>Meanwhile, the evaluation goes from <strong>0.2 to 3.4 for (a3 and then) Rd8</strong>.</li>
</ol>
<p>Thus, it seems like Rd8 cost black a drawn game rather than that Black didn't really have that much chance to draw(/win) from the start (of the endgame in the video).</p>
<p>What's going on?</p>
<p>Similar question: <a href="https://chess.stackexchange.com/questions/36803/akiba-rubinstein-vs-alexander-alekhine-1911-rook-endgame-the-mistake-here-is-rx">akiba rubinstein vs alexander alekhine 1911 rook endgame: the mistake here is Rxb5 right?</a></p>
 11144: <p>The mystery is easily solved if you just follow a few alternatives with the engine. The point is simply that if White comes to b4, the Rc5 gets another protection. This means that after exd5 Rxd5, White can march on with Ke4 as c5 is no longer hanging, and his activity wins in the long end (autoplay again). And cxd5 instead will immediately lead to zugzwang, and dxe4 is obviously (?) bad in any case. Thus not Rd8 is the cause of (probable) loss, but not blocking b4 in time.</p>
