Grease, oils, and even… skin flakes (eww!) from people can easily contaminate exposed Printed Circuit Boards (PCBs). Analog circuits especially are susceptible to oils. Bare wires too, hot solder can just slide right off. Think about the pins on the IC, oils will repel the hot solder. This is why finger cots are great, ESD Safe Antistatic Finger Cots from Botron are even better. non-ESD safe finger cots will build up a large static charge, whereas Botron’s Antistatic Finger Cots will not.