Technique to win this same colored bishop endgame

Question

The following endgame is a same-colored bishop endgame which I had on a game in Lichess. I tried for approximately 30 moves to try and win this game, but in the end, I got nothing more than a draw. I just felt that I was better due to white having 4 isolated pawns and 3 on light squares. Stockfish 11 evaluates the position as -4.3 at depth 40. The position in black to move. Please explain to me the technique to win this endgame.

Answer 1

The key here is zugzwang - White has an ideal defensive position at the moment, his king stops yours penetrating, his bishop covers the weak pawns on g4 and c4, and the pawn on a5 you can't easily get at is it is on a black square. BUT when white has to move he will either have to move his king (letting your king in), or move his bishop (leaving a pawn undefended) or move his a pawn (giving you an extra passed pawn)

So how can you take advantage of this? Well... if your bishop was on e6 and it was white's move he would be in zugzwang, and would either immediately drop a pawn (through a bishop or pawn move) or very soon afterwards (through a king move). Now note you can't just move your bishop straight to e6 as this would leave a position where you, not white, has the move. What you have to do is lose a move with the bishop - sometimes called triangulating with the bishop in reference to the similar idea with the King:

[Event ""]
[Site ""]
[Date "????.??.??"]
[Round ""]
[White ""]
[Black ""]
[Result "*"]
[FEN "8/1p6/5p2/P1p1k1p1/b1P1P1P1/4K3/4B3/8 b - - 0 1"]

1...Be8 
    ( 1...Bd7?! 2.Bd1 Be6 3.Be2 {And white is OK for the moment
    } )
    ( 1...Kd6?? {Trying to get to the a pawn} 2.e5+ Kxe5 3.Bf3 Kd6 4.Bxb7 )
2.Bf1 Bd7 
    {so losing a move}
3.Be2 Be6 
    {Now white has the move and has to give you something}
4.Bf3 
    ( 4.Kf3 Kd4 )
    ( 4.Kd3 Kf4 )
    ( 4.Kf2 {Stockfish's Choice} 4...Kd4 
        ( 4...Kxe4?? {Be Careful!} 5.Bf3+ )
    5.Bf3 Kxc4 6.e5 fxe5 7.Bxb7 Kb5 8.a6 Kb6 )
4...Bxc4 
    {and wins}
*

There's a free course at chessable (https://www.chessable.com/) called "Basic Endgames" which covers this, amongst many other things