Centurini's Position 1856
A same coloured bishop endgame study.
This position is analysed in Bernd Rosen's "Chess Endgame Training"
I have transcribed it into this diagram in an effort to clarify this mysterious sequence.
White's bishop first heads to b8 via a7, but gets prevented by Black's Ka6.
Then the white bishop goes to c5 forcing Black to move their bishop. (the king is still trying to prevent Ba7) The black bishop was avoiding deflection moves by the white bishop on the d8-h4 diagonal by camping on h2.
Next the manoeuvre Be7-d8 forces the king back to c6 to defend against Bc7.
Now the white bishop uses the deflection tactic on the d8-h4 diagonal to force their way through to the g1-a7 diagonal with tempo and so can reach a7 on the next move without the black king stopping it.
After white plays Bb8 the black bishop must switch to the g1-a7 diagonal to be able to cover the queening square from a7.
Once the black bishop reaches a7 though, it can no longer avoid the deflection move from the white bishop.
As Bernd Rosen points out: If the diagonal was one square longer black would be able to avoid the deflection and a draw would result.