A dead string bed shows up on the slice first

Players notice a racket is finished when the forehand starts flying, but the slice was telling them an hour earlier.

Strings do not fail all at once. They lose tension, they lose elasticity, and the polyester ones in particular go through a stage where they still look perfectly fine and no longer do what they used to. The question is which shot tells you first, and I do not think it is the forehand.

The forehand is forgiving of a tired string bed because a heavy topspin swing produces its own shape. If the strings give you a bit more power and grip the ball a bit less, the ball goes slightly longer and slightly flatter, and a player with a fast swing will unconsciously add a touch more brush and never notice. The correction is automatic and it hides the problem for a long time.

The slice has nowhere to hide. It is a low speed shot where almost all of the character comes from the interaction between the ball and the string bed, because you are not overwhelming the strings with racket head speed. When the bed goes dead, backspin drops, and a slice with less backspin sits up instead of skidding. The player feels it immediately as the shot floating, and usually blames their technique.

The drop volley is the same story and even more sensitive, which is why touch players change rackets far more often than baseliners with identical string breakage rates. It is not superstition. Their game is built on the part of the equipment that degrades first.

There is a practical test in this. Before a match, hit six slices and two drop shots rather than twenty forehands. If the slice is not biting, restring, whatever the calendar says. Twenty forehands will tell you nothing because your arm will have already adjusted for whatever is wrong.

The wider point is that equipment feedback is not evenly distributed across the shots in your game, and most players are monitoring their racket through the shot that is least able to report on it.

If your game has no touch shots in it at all, you are flying blind, and you will keep playing with dead strings until an error tells you.

By then you have lost a set explaining it to yourself.