Sometimes, bobby pins don't do what they're supposed to do. You want them to hold your hair in place, but gradually, throughout the day, they come loose. To get them to hold better, spray them with hairspray before styling your hair.
Photo by Hey Paul Studios
Beauty site Makeup.com explains:
Coating your bobby pins with a layer of hairspray will transform them into "sticky pins" and give them a better grip when you slide them into that carefully styled bouffant braid. If you don't want to spray them individually, you can place your bobby pins on a paper towel, spray, then pick up the paper towel on the edges and give them a little shake to distribute the product evenly. Then, just pin away!
I actually saw a stylist do this while I was getting a haircut, so I thought I'd give it a shot. It definitely does the trick. For more bobby pin tips, check out the full post at the link below.
The Bobby Pin Trick That Changes Everything [Makeup.com]