This is one of the most useful studies you can know. Everyone "knows" that a rook pawn that wants to queen needs a bishop of the color of the queening square, otherwise it's a draw because the king can sit on the queening square and not be forced away from, in this case, g7 and h8. A Troitsky study gives the example of when this is not true.
1.Be6 Ke7 If 1...Kf8 2.h6 Ke7 3.h7]2.h6 Kf6 3.Bf5 Kf7 4.Bh7 Keeping the king away from g6, g7 and g8. The only chance for Black is to get behind the pawn on g5. 4...Kf6 5.Kf4 Now, White, using the opposition, forces the king away and wins. 5...Kf7 6.Kf5 Ke7 7.Kg6 Kf8 8.Kf6 Ke8 9.Kg7 Thankfully, the white king was close enough to do the opposition work.