Consider a simple chess example:
Q is white Queen.
K, R is black King and black Rook respectively.
A B
1 . Q
2 . .
3 K .
4 . .
5 . .
6 R .
7 . .
8 . R
1,2...8 is the rank and A and B are the files of the chessboard.
Assume the king can only move horizontally for this example.
Here, if we search to depth 0, the best move should be Qxb8 (queen takes rook on B8)
But if we search for depth 2, then one line goes:
1. Qa1+ Kb3 2. Qxa6 (evaluation of the position +100 as rook is taken)
Second line:
1. Qxb8 Ra4 2. Qb1 (evaluation of the position +100 as rook is taken)
And since both have the same evaluation we select the first variation and play Qa1+ and let's say opposing player plays Kb3.
And now, if we again search to depth 2, same situation arise:
One line:
1. Qb1+ Ka3 2. Qxb8 (evaluation of the position +100 as rook is taken)
Second line:
1. Qxa6 Rb4 2. Qa1 (evaluation of the position +100 as rook is taken)
And again since both lines have the same evaluation we select the first variation and play Qb1+ and let's say opposing player plays Ka3.
And this will keep repeating and the queen will never capture the rook and just keep checking the king in the hope of capturing the rook in the next move but again repeats the same idea.
I hope this example makes it much clear what I am trying to say.