What it actually feels like
The comparison everybody reaches for is a cat scratch, and it is closer to a hot cat scratch that does not stop. But the useful thing to know is not the sensation, it is the shape of it over time: sharp and manageable at the start, dull and tiring in the middle, and then oddly fine at the end.
Placement changes the intensity far more than technique does. Ribs, sternum, the ditch of the elbow, the back of the knee, the feet and anywhere directly over bone with no padding are meaningfully harder. Outer arm, forearm, thigh and calf are meaningfully easier, and a first tattoo on one of those is not cowardice, it is sequencing.
The thing that is worse than the needle
Sitting still. Three hours of holding one arm in one position while somebody works on it is a physical task in its own right, and it is the part nobody warns you about. Your neck will hurt. Your supporting shoulder will hurt more than the tattoo.
Which is what the break is for, and why we schedule the booth for the whole day even on a three-hour piece. There is no clock in the room and nobody is waiting for the chair.
Bring
Headphones and something you have already seen or read. Concentration is not available at hour two. A charger. Food with sugar in it. One person, or nobody, both of which are fine.