The second serve is the shot that actually decides matches

First serve percentages fill the broadcast graphics while the point that gets replayed in a player's head is always the other one.

Nobody warms up their second serve. Watch the five minutes before a match and you will see thirty first serves hit flat and hard, then two apologetic kicks, then the coin toss. It is the shot with the most pressure attached to it and the least practice behind it, and I do not think that is an accident. It is unpleasant to practise.

The structural point is that a first serve is a free option. Miss it and nothing happens. Every incentive says hit it hard. The second serve carries the whole cost of failure, and because of that it gets hit at a speed chosen by anxiety rather than by tactics.

Which produces the pattern you see in every close match. A player who is comfortable is serving second serves into the body or wide to the backhand with real spin, and the return comes back short. A player who is nervous is serving into the middle of the box at a pace that any professional returner will step around and hit through. Same technique. Different intention, and the intention shows up on the scoreboard within three games.

Here is the opinion. I would rather see players lower first serve speed and raise the percentage than keep the current split, and the reason is not the free points on first serve. It is that a higher first serve percentage means fewer second serves, and the second serve is where the damage happens. Reducing exposure to your weakest shot is worth more than adding a fraction to your strongest.

The counterargument is real. A soft first serve invites attack too, and a returner who knows nothing is coming will stand inside the baseline all afternoon. Fine. The point is not to serve gently. It is that the optimisation everyone runs, maximise the value of the first serve, is being run on the wrong variable.

There is a returning side to this. Standing several metres behind the baseline on a second serve is a choice to give the server a free ball. It is defensible against a heavy kicker on a slow surface and it is close to indefensible on a fast one, where the correct answer is to move in and take the ball early even at the cost of some errors. The errors are visible. The pressure created is not.

Serve two hundred second serves a week, alone, at the end of a session when the legs are tired.

That is the whole coaching tip. Nobody wants it.