Rule 6 of 25 · Chapter I — Before You Move
Hold the club light enough to feel the head's weight and firm enough that you never need to regrip at the top.
Why this rule exists
A crushing grip tightens the forearms and shoulders, which slows the release and makes it hard to feel where the clubhead is. A grip that is too loose forces a small adjustment at the top of the backswing, and that regrip changes the face angle without you knowing. Either extreme costs you consistent face control, which is the difference between a strike and a near-miss.
In practice
Aim for a pressure where you could still waggle the club and sense the head, with the last three fingers of the lead hand doing most of the holding. Rate your grip out of ten before each swing and keep it in the middle range; if the club moves in your hands during the swing, tighten a notch. Fresh grips and dry gloves let you hold on lighter, so replace both before they get slick.
When it doesn't apply
Deep rough, wet grips and heavy lies all demand more pressure to stop the face turning through impact. Some strong players naturally play well with firm hands throughout — if your face control is good and your speed is not suffering, do not fix what is working.