Are you a new handquilter?
Are your hands/fingers compromised in any way? .... Arthritis/carpel tunnel/nerve damage
Are you using a very thin cotton or wool batting and good quality quilting cottons?
All these will affect your ability to handle the tiny size 12 needle. Many people start with a larger needle (smaller number, isn't that weird?) until they become adept at the stitch, maybe many quilts later.
I, who have been handquilting for many, many years, use a larger needle because I can't feel the needle in my hand with the nerve damage I have. My stitches are about 9 to the inch even with the larger needle.
We never started beginners on the #12 needle unless they were regular handwork sewers.
Jan in VA