This is a real basic concept that is often a problem that begins right at the beginning for players, but is overlooked, and takes root as a major handicap for future playing. We are talking about the right hand of the pick style player.
Here is the point. Most people tend to grip the pick to tight! They have A LOT of extra tension in their hand that they don't recognize as tension. It feels normal to them. Then, to make matters worse, when they contact the strings with the pick, for a note or a strum, they tighten their hand even more, without knowing it.
Do not do this! Look at your right hand as you play. Here are two tip-offs that you have extra tension: the fingers not holding the pick curl in to the hand, as if to make a fist, or the wrist presses itself on to the face of the guitar, while the unfortunate guitarist continues to play as well as they can under the circumstances. (Another sign will be pressing on the guitar with the pinky).
The fingers holding the pick, and indeed the whole right hand, must be trained to be a sensitive instrument that is always responding to the needs of each playing situation. If a harder attack is desired, the hold on the pick will increase slightly, but never more than necessary. You will never maintain that extra tension after it is not needed anymore.