The beginner grip that holds the racket face flat in front of you like a frying pan. It feels safe, but it locks your wrist and your rotation — leaving you little more than a straight poke.
The basic handshake grip — you hold the racket as if shaking someone's hand — is the base from which you play almost every shot. The panhandle grip turns the racket so the face points flat at the shuttle instead. It's tempting, because you can see the face and you meet the shuttle reliably. What it costs you is exactly the rotation that creates pace, and it makes backhands and delicate net play close to impossible. The fix isn't strength work, it's a grip change: hold loosely, put your thumb on the wide side of the handle for the backhand, and change early and deliberately — with practice it becomes automatic. The common misunderstanding: the problem isn't that this grip is wrong, it's that it stays your only one. One grip means one answer to every shuttle.